N 12. The skeletal system. The Muscular System


A human skeleton - (endoskeleton)


A human skeleton - (endoskeleton)

In biology, the skeleton (from Greek σκελετός, "dried-up") or skeletal system is the biological system providing physical support in living organisms. (By extension, non-biological outline structures such as gantries or buildings may also acquire skeletons.)

Types and classification

Skeletal systems are commonly divided into three types - external (an exoskeleton), internal (an endoskeleton), and fluid based (a hydrostatic skeleton), although hydrostatic skeletal systems may be classified separately from the other two, because they lack hardened support structures.

External skeletons

Large external systems support proportionally less weight than endoskeletons of the same size, thus many larger animals, such as the vertebrates, have internal skeletal systems. Examples of exoskeletons are found in arthropods and shellfish, in which the skeleton forms a hard shell-like covering protecting the internal organs.

The phyla Arthropoda and Mollusca both have exoskeletons. Since exoskeletons necessarily limit growth, phyla with exoskeletons have developed various solutions. Most mollusks have calcareous shells and, as they grow, the diameter of the shell is enlarged without altering its shape. On the other hand, arthropods shed their exoskeletons to grow, a process known as ecdysis (or molting). During molting the arthropod breaks down the old exoskeleton and then generates a new one, parts of which then harden, through various processes (such as calcification or sclerotization). An arthropod exoskeleton typically also has internal extensions, commonly referred to as an endoskeleton, although it is not a true endoskeleton.

Internal skeletons

An internal skeletal system consists of rigid (or semi-rigid) structures, within the body, moved by the muscular system. If the structures are mineralized or ossified, as they are in humans and other mammals, they are referred to as bones. Cartilage is another common component of skeletal systems, supporting and supplementing the skeleton. The human ear and nose are shaped by cartilage. Some organisms have a skeleton consisting entirely of cartilage and without any calcified bones at all, for example sharks. The bones or other rigid structures are connected by ligaments and connected to the muscular system via tendons.

Hydrostatic skeletons are similar to a water-filled balloon. Located internally in cnidarians (coral, jellyfish etc.) and annelids (leeches, earthworms etc.), among others, these animals can move by contracting the muscles surrounding the fluid-filled pouch, creating pressure within the pouch that causes movement. Animals such as earthworms use their hydrostatic skeletons to change their body shape, as they move forward, from long and thin to shorter and wider.

Skull classification

Amniotes, a group of animals that have an endoskeleton can also be further classed by their skeletons, specifically their skulls. The number of holes (temporal fenestra) in the top of their crania decide what class they fall into.


Human Skull Anatomy Pictures








The skeleton has six main functions:


The skeleton provides the framework which supports the body, allowing large animals to maintain their shape. And helps large animals to decrease its chance to have too much injury.


The bones of the skeleton provide an attachment surface for muscles, tendons and ligaments.


Movement in vertebrates is dependent on the skeletal muscles, which are attached to the skeleton by tendons. Without the skeleton to give leverage, movement would be greatly restricted.


The skeleton protects many vital organs: The skull protects the brain, the vertebral column protects the spinal cord, and the ribcage protects the lungs and the heart.

] Blood cell production

The skeleton is the site of haematopoiesis - the generation of blood cells, that takes place in red bone marrow (which is why bone marrow cancer is very often a terminal disease)


Bone also serves as a mineral storage deposit in which nutrients can be stored and retrieved. Calcium, especially, can be released by dissolution of bone tissue under the control of 1,25-dihydroxyvitamin D3 during periods of low calcium intake.


The human skeleton can be divided into the axial skeleton and the appendicular skeleton.

The axial skeleton has five areas and consists of 80 bones in a typical adult:

                     Skull (22)

                     Ossicles (bones of the middle ear) (6)

                     Hyoid bone (bone in the throat) (1)

                     Vertebral column (26)

                     Chest (25)

The appendicular skeleton has six areas and consists of 126 bones in a typical adult:

                     Shoulder girdle (4)

                     Arms (6)

                     Hands (54)

                     Pelvic girdle (2)

                     Legs (8)

                     Feet (52)

Human newborns have over 270 bones some of which fuse together into a longitudinal axis, the axial skeleton, to which the appendicular skeleton is attached.

Axial skeleton

Diagram of the axial skeleton


The axial skeleton consists of the 80 bones along the central axis of the human body. It is composed of six parts; the human skull, the ossicles of the middle ear, the hyoid bone of the throat, the rib cage, sternum and the vertebral column. The axial skeleton and the appendicular skeleton together form the complete skeleton.

Flat bones house the brain, spinal cord, and other vital organs. This article mainly deals with the axial skeletons of humans; however, it is important to understand the evolutionary lineage of the axial skeleton. The human axial skeleton consists of 80 different bones. It is the midial core of the body and connects the pelvis to the body, where the appendix skeleton attaches. As the skeleton grows older the bones get weaker with the exception of the skull. The skull remains strong to protect the brain from injury.




The word "Axial" is taken from the word "axis" and refers to the fact that the bones are located close to or along the central axis of the body.


Skull. The human skull is a bony structure, part of the skeleton, that is in the human head and which supports the structures of the face and forms a cavity for the brain.


The adult human skull is said to consist of two categorical parts of different embryological origins: The neurocranium and the viscerocranium. The neurocranium (or braincase) is a protective vault surrounding the brain and brain stem. The viscerocranium (also splanchnocranium or facial skeleton) is formed by the bones supporting the face.


Except for the mandible, all of the bones of the skull are joined together by sutures, synarthrodial (immovable) joints formed by bony ossification, with Sharpey's fibres permitting some flexibility.


Human skull side bones


Skull (22)

The lower inner surface of the neurocranium

        Cranial Bones (8)

        Parietal (2)

        Temporal (2)

        Frontal (1)

        Occipital (1)

        Ethmoid (1)

        sphenoid (1)

Various sources provide different numbers for the count of constituent bones of the human neuro- and viscerocranium. The reasons for such counting discrepancies are numerous. Different textbooks classify the bones of the human skull differently, e.g. they may (also) include (parts of) bones that are ordinarily considered neurocranial bones in their list of facial bones. Some textbooks count paired bones (where there is one bone on each side) only once instead of twice. Some sources describe the maxilla's left and right parts as two bones. Likewise, the palatine bone is also sometimes described as two bones. The hyoid bone is usually not considered part of the skull, as it does not articulate with any other bones, but some sources include it. Some sources include the ossicles, three of which on each side are encased within the temporal bones, though these are also usually not considered part of the skull. Extra sutural bones may also variably be present, but they are not counted. For all of these reasons, it may not be easy[2] to reach agreement on an authoritative bone count for the neuro- and viscerocranium and the human skull. However, such discrepancies between various sources are only differences in how to classify and/or describe the anatomy of the human skull, and regardless of what classification/description is used, the basic anatomy remains the same. With that in mind, as one possible classification, the human skull could for example be said to consist of twenty two bones: Eight bones of the neurocranium (occipital bone, 2 temporal bones, 2 parietal bones, sphenoid bone, ethmoid bone, frontal bone), and fourteen bones of the viscerocranium (vomer, 2 conchae, 2 nasal bones, 2 maxilla, mandible, 2 palatine bone, 2 zygomatic bones, 2 lacrimal bones).


The skull also contains the sinus cavities, which are air-filled cavities lined with respiratory epithelium, which also lines the large airways. The exact functions of the sinuses are debatable; they contribute to lessening the weight of the skull with a minimal reduction in strength, they contribute to resonance of the voice, and assist in the warming and moistening of air drawn in through the nasal cavity.

Development of the skull

The lower inner surface of the neurocranium- 11 weeks' fertilization age


The skull is a complex structure; its bones are formed both by intramembranous and endochondral ossification. The skull roof, comprising the bones of the splanchnocranium (face) and the sides and roof of the neurocranium, is formed by intramembranous (or dermal) ossification, though the temporal bones are formed by endochondral ossification. The endocranium, the bones supporting the brain (the occipital, sphenoid, and ethmoid) are largely formed by endochondral ossification. Thus frontal and parietal bones are purely membranous.[3] The geometry of the cranial base and its fossas: anterior, middle and posterior changes rapidly, especially during the first trimester of pregnancy. The first trimester is crucial for development of skull defects.[4]


At birth, the human skull is made up of 44 separate bony elements. As growth occurs, many of these bony elements gradually fuse together into solid bone (for example, the frontal bone). The bones of the roof of the skull are initially separated by regions of dense connective tissue called "fontanels". There are six fontanels: one anterior (or frontal), one posterior (or occipital), two sphenoid (or anterolateral), and two mastoid (or posterolateral). At birth these regions are fibrous and moveable, necessary for birth and later growth. This growth can put a large amount of tension on the "obstetrical hinge", which is where the squamous and lateral parts of the occipital bone meet. A possible complication of this tension is rupture of the great cerebral vein of Galen. As growth and ossification progress, the connective tissue of the fontanelles is invaded and replaced by bone creating sutures. The five sutures are the two squamous, one coronal, one lambdoid, and one sagittal sutures. The posterior fontanel usually closes by eight weeks, but the anterior fontanel can remain open up to eighteen months. The anterior fontanel is located at the junction of the frontal and parietal bones; it is a "soft spot" on a baby's forehead. Careful observation will show that you can count a baby's heart rate by observing his or her pulse pulsing softly through the anterior fontanel.




If the brain is bruised or injured it can be life-threatening. Normally the skull protects the brain from damage through its hard unyieldingness; the skull is one of the least deformable structures found in nature with it needing the force of about 1 ton to reduce the diameter of the skull by 1 cm.[5] In some cases, however, of head injury, there can be raised intracranial pressure through mechanisms such as a subdural haematoma. In these cases the raised intracranial pressure can cause herniation of the brain out of the foramen magnum ("coning") because there is no space for the brain to expand; this can result in significant brain damage or death unless an urgent operation is performed to relieve the pressure. This is why patients with concussion must be watched extremely carefully.


Dating back to Neolithic times, a skull operation called trepanation was sometimes performed. This involved drilling holes in the cranium. Examination of skulls from this period reveals that the "patients" sometimes survived for many years afterward. It seems likely that trepanation was performed for ritualistic or religious reasons and not only as an attempted life-saving technique.


Craniometry and morphology of human skulls


Like the face of a living individual, a human skull and teeth can also tell, to a certain degree, the life history and origin of its owner. Forensic scientists and archaeologists use metric and nonmetric traits to estimate what the bearer of the skull looked like. When a significant amount of bones are found, such as at Spitalfields in the UK and Jōmon shell mounds in Japan, osteologists can use traits, such as the proportions of length, height and width, to know the relationships of the population of the study with other living or extinct populations.


The German physician Franz Joseph Gall in around 1800 formulated the theory of phrenology, which attempted to show that specific features of the skull are associated with certain personality traits or intellectual capabilities of its owner. This theory is now considered to be obsolete.


Sexual dimorphism


In the past, specifically in the mid-nineteenth century, anthropologists found it crucial to distinguish between male and female skulls. An anthropolgist of the time, McGrigor Allan, argued that the female brain was similar to that of an animal[6] . This allowed anthropologists to declare that women were in fact more emotional and less like their rational male counterparts. McGrigor then concluded that womens brains were more analogous to infants, thus deeming them inferior at the time[7] . To further these claims of female inferiority and silence the feminists of the time, other anthropolgists joined in on the studies of the female skull. These cranial measurements are the basis of what is known as craniology. These cranial measurements were also used to draw a connection between females and Negroes. French craniolgist, F. Pruner, went on to describe this relationship as: The Negro resemble[ing] the female in his love for children, his family, and his cabin"[8] . Pruner also went on to say that the negro is what the female is to the white man, a loving being and a being of pleasure[9] . New forms of cranial measurement continued to progress well into the early twentieth century in a effort to further implement the sexual dimorphism between male and female skulls.


Research today shows that while in early life there is little difference between male and female skulls, in adulthood male skulls tend to be larger and more robust than female skulls, which are lighter and smaller, with a cranial capacity about 10 percent less than that of the male.[10] However, new studies show that women's skulls are thicker and thus men may be more susceptible to head injury than women.[11][12] The male body is larger than the female body, which accounts for the larger size of the male skull; proportionally, the male skull is about the same size as the female skull. Male skulls typically have more prominent supraorbital ridges, a more prominent glabella, and more prominent temporal lines. Female skulls generally have rounder orbits, and narrower jaws. Male skulls on average have larger, broader palates, squarer orbits, larger mastoid processes, larger sinuses, and larger occipital condyles than those of females. Male mandibles typically have squarer chins and thicker, rougher muscle attachments than female mandibles.

A cross-section of a skull

Male human skull

Child viscerocranium

Anterior, middle and posterior fossa

Bones of human skull Endobasis-resistances beams

Endobasis-resistances beams

Endobasis-resistances nodes

Auditory Ossicles


Ossicles (6 )

        Malleus (2)

        Incus (2)

        Stapes (2)


Hyoid bone


Hyoid bone U-shape bone located in the neck. It anchors the tongue and is associated with swallowing.


Vertebral column

The vertebral column, also known as backbone or spine, is a bony structure found in Vertebrates. It is formed from the vertebrae. There are normally thirty-three (33) vertebrae in humans, including the five that are fused to form the sacrum (the others are separated by intervertebral discs) and the four coccygeal bones that form the tailbone. The upper three regions comprise the remaining 24, and are grouped under the names cervical (7 vertebrae), thoracic (12 vertebrae) and lumbar (5 vertebrae), according to the regions they occupy. This number is sometimes increased by an additional vertebra in one region, or it may be diminished in one region, the deficiency often being supplied by an additional vertebra in another. The number of cervical vertebrae is, however, very rarely increased or diminished.[2]

Vertebral column

Divisions of Spinal Segments

egmental Spinal Cord Level and Function





Neck flexors


Neck extensors

C3, C4, C5

Supply diaphragm (mostly C4)

C5, C6

Shoulder movement, raise arm (deltoid); flexion of elbow (biceps); C6 externally rotates the arm (supinates)

C6, C7

Extends elbow and wrist (triceps and wrist extensors); pronates wrist

C7, T1

Flexes wrist

C7, T1

Supply small muscles of the hand

T1 -T6

Intercostals and trunk above the waist


Abdominal muscles

L1, L2, L3, L4

Thigh flexion

L2, L3, L4

Thigh adduction

L4, L5, S1

Thigh abduction

L5, S1, S2

Extension of leg at the hip (gluteus maximus)

L2, L3, L4

Extension of leg at the knee (quadriceps femoris)

L4, L5, S1, S2

Flexion of leg at the knee (hamstrings)

L4, L5, S1

Dorsiflexion of foot (tibialis anterior)

L4, L5, S1

Extension of toes

L5, S1, S2

Plantar flexion of foot

L5, S1, S2

Flexion of toes


With the exception of the first and second cervical, the true or movable vertebrae (the upper three regions) present certain common characteristics that are best studied by examining one from the middle of the thoracic region.

Vertebral Column (26)

        Cervical vertebrae (7)

        Thoracic vertebrae (12)

        Lumbar vertebrae (5)

        Sacrum (1) (5 at birth, later fused in adult stage)

        Coccyx (1) (4 at birth, later fused to form one single bone, varies between 3-5)

Structure of individual vertebrae

A diagram of a human thoracic vertebra. Notice the articulations for the ribs

Oblique view of cervical vertebrae.


A typical vertebra consists of two essential parts: an anterior (front) segment, which is the vertebral body; and a posterior part the vertebral (neural) arch which encloses the vertebral foramen. The vertebral arch is formed by a pair of pedicles and a pair of laminae, and supports seven processes, four articular, two transverse, and one spinous, the latter also being known as the neural spine.


When the vertebrae are articulated with each other, the bodies form a strong pillar for the support of the head and trunk, and the vertebral foramina constitute a canal for the protection of the medulla spinalis (spinal cord). In between every pair of vertebrae are two apertures, the intervertebral foramina, one on either side, for the transmission of the spinal nerves and vessels.


Two transverse processes and one spinous process are posterior to (behind) the vertebral body. The spinous process comes out the back, one transverse process comes out the left, and one on the right. The spinous processes of the cervical and lumbar regions can be felt through the skin.


Superior and inferior articular facets on each vertebra act to restrict the range of movement possible. These facets are joined by a thin portion of the neural arch called the pars interarticularis.




Viewed laterally the vertebral column presents several curves, which correspond to the different regions of the column, and are called cervical, thoracic, lumbar, and pelvic.


The cervical curve, convex forward, begins at the apex of the odontoid (tooth-like) process, and ends at the middle of the second thoracic vertebra; it is the least marked of all the curves.


The thoracic curve, concave forward, begins at the middle of the second and ends at the middle of the twelfth thoracic vertebra. Its most prominent point behind corresponds to the spinous process of the seventh thoracic vertebra. This curve is known as a tt curve.


The lumbar curve is more marked in the female than in the male; it begins at the middle of the last thoracic vertebra, and ends at the sacrovertebral angle. It is convex anteriorly, the convexity of the lower three vertebrae being much greater than that of the upper two. This curve is described as a lordotic curve.


The pelvic curve begins at the sacrovertebral articulation, and ends at the point of the coccyx; its concavity is directed downward and forward.


The thoracic and pelvic curves are termed primary curves, because they alone are present during fetal life. The cervical and lumbar curves are compensatory or secondary, and are developed after birth, the former when the child is able to hold up its head (at three or four months) and to sit upright (at nine months), the latter at twelve or eighteen months, when the child begins to walk.



Orientation of vertebral column on surface. T3 is at level of medial part of spine of scapula. T7 is at inferior angle of the scapula. L4 is at highest point of iliac crest. S2 is at the level of posterior superior iliac spine. Furthermore, C7 is easily localized as a prominence at the lower part of the neck.[3]


There are a total of 33 vertebrae in the vertebral column, if assuming 4 coccygeal vertebrae.


The individual vertebrae, named according to region and position, from superior to inferior, are:

        Cervical: 7 vertebrae (C1C7)

        Thoracic: 12 vertebrae (T1T12)

        Lumbar: 5 vertebrae (L1L5)

        Sacral: 5 (fused) vertebrae (S1S5)

        Coccygeal: 4 (35) (fused) vertebrae (Tailbone)




There are seven (7) cervical bones (but 8 cervical spinal nerves) and these bones are, in general, small and delicate. Their spinous processes are short (with the exception of C2 and C7, which have palpable spinous processes). Numbered top-to-bottom from C1-C7, atlas (C1) and axis (C2), are the vertebrae that allow the neck and head so much movement. For the most part, the atlanto-occipital joint allows the skull to move up and down, while the atlanto-axial joint allows the upper neck to twist left and right. The axis also sits upon the first intervertebral disk of the spinal column. All mammals except manatees and sloths have seven cervical vertebrae, whatever the length of the neck.


Cervical vertebrae possess transverse foramina to allow for the vertebral arteries to pass through on their way to the foramen magnum to end in the circle of Willis. These are the smallest, lightest vertebrae and the vertebral foramina are triangular in shape. The spinous processes are short and often bifurcated (the spinous process of C7, however, is not bifurcated, and is substantially longer than that of the other cervical spinous processes).


The term cervicothoracic is often used to refer to the cervical and thoracic vertebrae together, and sometimes also their surrounding areas.




The twelve (12) thoracic bones and their transverse processes have surfaces that articulate with the ribs. Some rotation can occur between the thoracic vertebrae, but their connection with the rib cage prevents much flexion or other excursion. They may also be known as 'dorsal vertebrae', in the human context.


Bodies are roughly heart-shaped and are about as wide anterio-posterioly as they are in the transverse dimension. Vertebral foramina are roughly circular in shape.


The term thoracolumbar is sometimes used to refer to the thoracic and lumbar vertebrae together, and sometimes also their surrounding areas.




These five (5) vertebrae are very robust in construction, as they must support more weight than other vertebrae. They allow significant flexion, extension and moderate lateral flexion (sidebending). The discs between these vertebrae create a lumbar lordosis (curvature that is concave posteriorly) in the human spine.


The term lumbosacral is often used to refer to the lumbar and sacral vertebrae together, and sometimes also their surrounding areas.




There are five (5) vertebrae (S1-S5) which are fused in maturity, with no intervertebral discs. The 5 fused bones are collectively known as the sacrum.




There are usually four (4) and rarely 3 or 5 vertebrae (Co1-Co5), with no intervertebral discs. Many animals have a greater number of "tail vertebrae," and, in animals, they are more commonly known as "caudal vertebrae." Pain at the coccyx (tailbone) is known as coccydynia.




The striking segmented pattern of the human spine is established during embryogenesis when the precursor of the vertebrae, the somites, are rhythmically added to the forming posterior part of the embryo. In humans, somite formation begins around the third week post-fertilization and continues until a total of around 52 somites are formed. The somites are epithelial spheres that contain the precursors of the vertebrae, the ribs, the skeletal muscles of the body wall and limbs, and the dermis of the back. The periodicity of somite distribution and production is thought to be imposed by a molecular oscillator or clock acting in cells of the presomitic mesoderm (PSM). Somites form soon after the beginning of gastrulation, on both sides of the neural tube from a tissue called the presomitic mesoderm (PSM). The PSM is part of the paraxial mesoderm and is generated caudally by gastrulation when cells ingress through the primitive streak, and later, through the tail bud. Soon after their formation, somites become subdivided into the dermomyotome dorsally, which gives rise to the muscles and dermis, and the sclerotome ventrally, which will form the spine components. Sclerotomes become subvidided into an anterior and a posterior compartment. This subdivision plays a key role in the definitive patterning of vertebrae that form when the posterior part of one somite fuses to the anterior part of the consecutive somite during a process termed resegmentation. Disruption of the somitogenesis process in humans results in diseases such as congenital scoliosis. So far, the human homologues of three genes associated to the mouse segmentation clock (MESP2, DLL3 and LFNG) have been shown to be mutated in human patients with human congenital scoliosis suggesting that the mechanisms involved in vertebral segmentation are conserved across vertebrates. In humans the first four somites are incorporated in the basi-occipital bone of the skull and the next 33 somites will form the vertebrae.[6] The remaining posterior somites degenerate. During the fourth week of embryonic development, the sclerotomes shift their position to surround the spinal cord and the notochord. The sclerotome is made of mesoderm and originates from the ventromedial part of the somites. This column of tissue has a segmented appearance, with alternating areas of dense and less dense areas.[citation needed]


As the sclerotome develops, it condenses further eventually developing into the vertebral body. Development of the appropriate shapes of the vertebral bodies is regulated by HOX genes.


The less dense tissue that separates the sclerotome segments develop into the intervertebral discs.


The notochord disappears in the sclerotome (vertebral body) segments, but persists in the region of the intervertebral discs as the nucleus pulposus. The nucleus pulposus and the fibers of the annulus fibrosus make up the intervertebral disc.


The primary curves (thoracic and sacral curvatures) form during fetal development. The secondary curves develop after birth. The cervical curvature forms as a result of lifting the head and the lumbar curvature forms as a result of walking.

Unfused arch of C1 at CT.


There are various defects associated with vertebral development. Scoliosis will result in improper fusion of the vertebrae. In Klippel-Feil anomaly patients have two or more cervical vertebrae that are fused together, along with other associated birth defects. One of the most serious defects is failure of the vertebral arches to fuse. This results in a condition called spina bifida. There are several variations of spina bifida that reflect the severity of the defect.



Anterior surface

The vertebrae may be used as vertical reference points to describe the locations of the organs of the trunk, such as with the transpyloric line (seen at body of L1). If not else specified, it is usually the middle of the vertebral body that is used as reference, although the palpable spinous processes may be located considerably lower.


When viewed from in front, the width of the bodies of the vertebrae is seen to increase from the second cervical to the first thoracic; there is then a slight diminution in the next three vertebrae; below this there is again a gradual and progressive increase in width as low as the sacrovertebral angle. From this point there is a rapid diminution, to the apex of the coccyx.


Posterior surface

Orientation of the rib cage on the vertebral column


The posterior surface of the vertebral column presents in the median line the spinous processes. In the cervical region (with the exception of the second and seventh vertebrae) these are short and horizontal, with bifid extremities. In the upper part of the thoracic region they are directed obliquely downward; in the middle they are almost vertical, and in the lower part they are nearly horizontal. In the lumbar region they are nearly horizontal. The spinous processes are separated by considerable intervals in the lumbar region, by narrower intervals in the neck, and are closely approximated in the middle of the thoracic region. Occasionally one of these processes deviates a little from the median line a fact to be remembered in practice, as irregularities of this sort are attendant also on fractures or displacements of the vertebral column. On either side of the spinous processes is the vertebral groove formed by the laminae in the cervical and lumbar regions, where it is shallow, and by the laminae and transverse processes in the thoracic region, where it is deep and broad; these grooves lodge the deep muscles of the back. Lateral to the vertebral grooves are the articular processes, and still more laterally the transverse processes. In the thoracic region, the transverse processes stand backward, on a plane considerably behind that of the same processes in the cervical and lumbar regions. In the cervical region, the transverse processes are placed in front of the articular processes, lateral to the pedicles and between the intervertebral foramina. In the thoracic region they are posterior to the pedicles, intervertebral foramina, and articular processes. In the lumbar region they are in front of the articular processes, but behind the intervertebral foramina.


Lateral surfaces


The lateral surfaces are separated from the posterior surface by the articular processes in the cervical and lumbar regions, and by the transverse processes in the thoracic region. They present, in back, the sides of the bodies of the vertebrae, marked in the thoracic region by the facets for articulation with the heads of the ribs. More posteriorly are the intervertebral foramina, formed by the juxtaposition of the vertebral notches, oval in shape, smallest in the cervical and upper part of the thoracic regions, and gradually increasing in size to the last lumbar. They transmit the special spinal nerves and are situated between the transverse processes in the cervical region, and in front of them in the thoracic and lumbar regions.

Vertebral canal


The vertebral canal follows the different curves of the column; it is large and triangular in those parts of the column which enjoy the greatest freedom of movement, such as the cervical and lumbar regions; and is small and rounded in the thoracic region, where motion is more limited.




Occasionally the coalescence of the laminae is not completed, and consequently a cleft is left in the arches of the vertebrae, through which a protrusion of the spinal membranes (dura mater and arachnoid), and generally of the spinal cord (medulla spinalis) itself, takes place, constituting the malformation known as spina bifida. This condition is most common in the lumbosacral region, but it may occur in the thoracic or cervical region, or the arches throughout the whole length of the canal may remain incomplete.


The following abnormal curvatures may occur in some people:

Kyphosis is an exaggerated kyphotic (posterior) curvature in the thoracic region. This produces the so-called "humpback" or "dowager's hump", a condition commonly observed in osteoporosis.

Lordosis is an exaggerated lordotic (anterior) curvature of the lumbar region, "swayback". Temporary lordosis is common among pregnant women.

Retrolisthesis is a posterior displacement of one vertebral body with respect to the adjacent vertebral segment to a degree less than a luxation (dislocation).

Scoliosis, lateral curvature, is the most common abnormal curvature, occurring in 0.5% of the population. It is more common among females and may result from unequal growth of the two sides of one or more vertebrae. It can also be caused by pulmonary atelectasis (partial or complete deflation of one or more lobes of the lungs) as observed in asthma or pneumothorax.











The spinal cord nested in the vertebral column.

Relation of the vertebral column to the surrounding muscles.


Thoracic cage (27)

        Sternum (3) - Manubrium (1) Body of sternum (1) Xiphoid process (1)

        Ribs (24)

The appendicular skeleton is composed of 126 bones in the human body. The word appendicular is the adjective of the noun appendage, which itself means a part that is joined to something larger. Functionally it is involved in locomotion (Lower limbs) of the axial skeleton and manipulation of objects in the environment (Upper limbs).


The appendicular skeleton forms during development from cartlilage, by the process of endochondral ossification.


The appendicular skeleton is divided into six major regions:


1) Pectoral Girdles (4 bones) - Left and right Clavicle (2) and Scapula (2).

Left and right clavicle: in human anatomy, the clavicle or collarbone is a long bone of short length that serves as a strut between the scapula and the sternum. It is the only long bone in the body that lies horizontally. It makes up part of the shoulder and the pectoral girdle and is palpable in all people, and, in people who have less fat in this region, the location of the bone is clearly visible as it creates a bulge in the skin. It receives its name from the Latin: clavicula ("little key") because the bone rotates along its axis like a key when the shoulder is abducted.

Bone: Clavicle

Human anatomy

Right clavicle from below, and from above.

Left clavicle from above, and from below.


The clavicle is a doubly curved short bone that connects the arm (upper limb) to the body (trunk), located directly above the first rib. It acts as a strut to keep the scapula in place so the arm can hang freely. Medially, it articulates with the manubrium of the sternum (breast-bone) at the sternoclavicular joint. At its lateral end it articulates with the acromion of the scapula (shoulder blade) at the acromioclavicular joint. It has a rounded medial end and a flattened lateral end.


From the roughly pyramidal sternal end, each clavicle curves laterally and anteriorly for roughly half its length. It then forms a smooth posterior curve to articulate with a process of the scapula (acromion). The flat acromial end of the clavicle is broader than the sternal end. The acromial end has a rough inferior surface that bears prominent line, Trapezoid line and a small rounded projection, Conoid tubercle. These surface features are attachment sites for muscles and ligaments of the shoulder.


It can be divided into three parts: medial end, lateral end and shaft.


Medial end


The medial end is the quadrangular and articulates with the clavicular notch of the menubrium sterni to form the sternoclavicular joint. The articular surface extends to the inferior aspect for attachment with the first costal cartilage.


It gives attachments to:

fibrous capsule joint all around

articular disc superoposteriorly

interclavicular ligament superiorly


Lateral end


The lateral end is flat from above downward. It bears a facet for attachment to the acromion process of the scapula, forming the acromioclavicular joint. The area surrounding the joint gives an attachment to the joint capsule.




The shaft is divided into medial 2/3 and lateral 1/3. The medial 2/3 is thicker than the lateral 1/3.


Medial 2/3 of the shaft


The medial 2/3 of the shaft has four surfaces and no borders.


The anterior surface is convex forward and gives origin to pectoralis major. Posterior surface is smooth and gives origin to sternohyoid muscle at its medial end. Superior surface is rough at its medial part and gives origin to sternocleidomastoid muscle . Inferior surface has an oval impression at its medial end for costoclavicular ligament. At the lateral side of inferior surface, there is a subclavian groove for insertion of subclavius muscle. At the lateral side of subclavian groove, nutrient foramen lies. The medial part is quadangular in shape where it makes a joint with the manubrium of the sternum at sternoclavicular joint. The margins of subclavian groove gives attachment to the clavipectoral fascia.


Lateral 1/3 of the shaft


The lateral 1/3 of the shaft has two borders and two surfaces.


The Anterior border is concave forward and gives origin to the deltoid muscle. The Posterior border is convex backward and gives attachment to the trapezius muscle . The Superior surface is subcutaneous. The Inferior surface has a ridge called the trapezoid line and a tubercle; the conoid tubercle for attachment with the trapezoid and the conoid part of the coracoclavicular ligament that serves to connect the clavicle with the coracoid process of the scapula.




Muscles and ligaments that attach to the clavicle include:

Attachment on clavicle


Other attachment

Superior surface and anterior border


Deltoid muscle

deltoid tubercle, anteriorly on the lateral third


Superior surface

Trapezius muscle

posteriorly on the lateral third


Inferior surface


Subclavius muscle

subclavian groove

Inferior surface


Conoid ligament (the medial part of the coracoclavicular ligament)

conoid tubercle

Inferior surface

Trapezoid ligament (the lateral part of the coracoclavicular ligament)

trapezoid line

Anterior border


Pectoralis major muscle

medial third (rounded border)

Posterior border


Sternocleidomastoid muscle (clavicular head)

superiorly, on the medial third

Posterior border


Sternohyoid muscle

inferiorly, on the medial third

Posterior border

Trapezius muscle

lateral third

The levator claviculae muscle, present in 23% of people, originates on the transverse processes of the upper cervical vertebrae and is inserted in the lateral half of the clavicle.



The clavicle serves several functions:

It serves as a rigid support from which the scapula and free limb (arm) are suspended; an arrangement that keeps the upper limb away from the thorax so that the arm has maximum range of movement. Acting as flexible, crane-like strut, it allows the scapula to move freely on the thoracic wall.

Covering the cervicoaxillary canal, it protects the neurovascular bundle that supplies the upper limb.

Transmits physical impacts from the upper limb to the axial skeleton.




The clavicle is the first bone to begin the process of ossification (laying down of minerals onto a preformed matrix) during development of the embryo, during the 5th and 6th weeks of gestation. However, it is one of the last bones to finish ossification at about 2125 years of age, and a study measuring 748 males and 252 females saw a difference in clavicle length between age groups 18-20 and 21-25 of about 6 and 5 mm (0.24 and 0.20 in) for males and females respectively. Its lateral end is formed by intramembranous ossification while medially it is formed by endochondral ossification. It consists of a mass of cancellous bone surrounded by a compact bone shell. The cancellous bone forms via two ossification centres, one medial and one lateral, which fuse later on. The compact forms as the layer of fascia covering the bone stimulates the ossification of adjacent tissue. The resulting compact bone is known as a periosteal collar.


Even though it is classified as a long bone, the clavicle has no medullary (bone marrow) cavity like other long bones, though this is not always true.[citation needed] It is made up of spongy (trabecular) bone with a shell of compact bone. It is a dermal bone derived from elements originally attached to the skull.




The shape of the clavicle varies more than most other long bones. It is occasionally pierced by a branch of the supraclavicular nerve. In males it is thicker and more curved and the sites of muscular attachments are more pronounced. The right clavicle is usually stronger and shorter than the left clavicle. In females the clavicle is thinner, smoother and lighter than that of males. Clavicle form is a reliable criterion for sex determination.


The collarbones are sometimes partly or completely absent in cleidocranial dysostosis.


Common clavicle injuries

Acromioclavicular dislocation ("AC Separation")

Clavicle fractures

Degeneration of the clavicle


Sternoclavicular dislocations


Evolutionary variation


The clavicle first appears as part of the skeleton in primitive bony fish, where it is associated with the pectoral fin; they also have a bone called the cleithrum. In such fish, the paired clavicles run behind and below the gills on each side, and are joined by a solid symphysis on the fish's underside. They are, however, absent in cartilagenous fish and in the vast majority of living bony fish, including all of the teleosts.


The earliest tetrapods retained this arrangement, with the addition of a diamond-shaped interclavicle between the base of the clavicles, although this is not found in living amphibians. The cleithrum disappeared early in the evolution of reptiles, and is not found in any living amniotes, but the interclavicle is present in most modern reptiles, and also in monotremes. In modern forms, however, there are a number of variations from the primitive pattern. For example, crocodilians and salamanders lack clavicles altogether (although crocodilians do retain the interclavicle), while in turtles, they form part of the armoured plastron.


In birds, the clavicles and interclavicle have fused to form a single Y-shaped bone, the furcula or "wishbone".


The interclavicle is absent in marsupials and placental mammals. In many mammals, the clavicles are also reduced, or even absent, to allow the scapula greater freedom of motion, which may be useful in fast-running animals.


Though a number of fossil hominin (humans and chimpanzees) clavicles have been found, most of these are mere segments offering limited information on the form and function of the pectoral girdle. One exception is the clavice of AL 333x6/9 attributed to Australopithecus afarensis which has a well-preserved sternal end. One interpretation of this specimen, based on the orientation of its lateral end and the position of the deltoid attachment area, suggests that this clavicle is distinct from those found in extant apes (including humans), and thus that the shape of the human shoulder dates back to less than 3 to 4 million years ago. However, analyses of the clavicle in extant primates suggest that the low position of the scapula in humans is reflected mostly in the curvature of the medial portion of the clavicle rather than the lateral portion. This part of the bone is similar in A. afarensis and it is thus possible that this species had a high shoulder position similar to that in modern humans.

Human arm bones diagram

Diagram of the human shoulder joint

Sternoclavicular articulation. Anterior view.

The left shoulder and acromioclavicular joints, and the proper ligaments of the scapula.

Muscles of the neck. Lateral view.

Muscles of the neck. Anterior view.

Anterolateral view of head and neck.

Front view of neck.



Scapula: In anatomy, the scapula (Medical Latin), or shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone).


The scapula forms the posterior (back) located part of the shoulder girdle. In humans, it is a flat bone, roughly triangular in shape, placed on a posterolateral aspect of the thoracic cage.

A posterior view of the thorax (scapula shown in red.)


Costal (Front, Ventral, Anterior)


The costal or ventral surface [Fig. 1] presents a broad concavity, the subscapular fossa.

1. Subscapular fossa

2. Glenoid cavity

3. Coracoid process

4. Acromion

5. Superior border

6. Scapular notch

7. Superior angle

8. Medial border

9. Inferior angle

10. Lateral border

11. Infraglenoid tubercle

Dorsal (Back, Posterior)


The dorsal surface [Fig. 2] is arched from above downward, and is subdivided into two unequal parts by the spine; the portion above the spine is called the supraspinous fossa, and that below it the infraspinous fossa.

The supraspinous fossa, the smaller of the two, is concave, smooth, and broader at its vertebral than at its humeral end; its medial two-thirds give origin to the Supraspinatus.

The infraspinous fossa is much larger than the preceding; toward its vertebral margin a shallow concavity is seen at its upper part; its center presents a prominent convexity, while near the axillary border is a deep groove which runs from the upper toward the lower part. The medial two-thirds of the fossa give origin to the Infraspinatus; the lateral third is covered by this muscle.


The dorsal surface is marked near the axillary border by an elevated ridge, which runs from the lower part of the glenoid cavity, downward and backward to the vertebral border, about 2.5 cm above the inferior angle.


The ridge serves for the attachment of a fibrous septum, which separates the Infraspinatus from the Teres major and Teres minor.


The surface between the ridge and the axillary border is narrow in the upper two-thirds of its extent, and is crossed near its center by a groove for the passage of the scapular circumflex vessels; it affords attachment to the Teres minor.


The costal surface superior of the scapula is the origin of 1st digitation for the serratus anterior origin. The broad and narrow portions above alluded to are separated by an oblique line, which runs from the axillary border, downward and backward, to meet the elevated ridge: to it is attached a fibrous septum which separates the Teres muscles from each other.


Its lower third presents a broader, somewhat triangular surface, which gives origin to the Teres major, and over which the Latissimus dorsi glides; frequently the latter muscle takes origin by a few fibers from this part.

Figure 1 : Left scapula. Costal surface.

The medial two-thirds of this fossa are marked by several oblique ridges, which run lateralward and upward. The ridges give attachment to the tendinous insertions, and the surfaces between them to the fleshy fibers, of the Subscapularis. The lateral third of the fossa is smooth and covered by the fibers of this muscle.


At the upper part of the fossa is a transverse depression, where the bone appears to be bent on itself along a line at right angles to and passing through the center of the glenoid cavity, forming a considerable angle, called the subscapular angle; this gives greater strength to the body of the bone by its arched form, while the summit of the arch serves to support the spine and acromion.

1. Supraspinatous fossa

2. Spine

3. Infraspinatous fossa

4. Superior border

5. Superior angle

6. Medial border

7. Inferior angle

8. Lateral border

9. Lateral angle

10. Acromion

11. Coracoid process

12. Orgin of teres major muscle

13. Orgin of teres minor muscle

Figure 2 : Left scapula. Dorsal surface.



There are three borders of the scapula:

The superior border is the shortest and thinnest; it is concave, and extends from the medial angle to the base of the coracoid process. It is referred to as the cranial border in animals.

The axillary border (or "lateral border") is the thickest of the three. It begins above at the lower margin of the glenoid cavity, and inclines obliquely downward and backward to the inferior angle. It is referred to as the caudal border in animals.

The vertebral border (or "medial border") is the longest of the three, and extends from the medial to the inferior angle. It is referred to as the dorsal border in animals.




There are 3 angles

        The superior angle is covered by trapezius.

        The inferior angle is covered by latissimus dorsi. It moves forwards round the chest when the arm is abducted.

        The lateral or glenoid angle is broad and bears the glenoid cavity or fossa, which is directed forward, laterally and slightly upwards.


The acromion


The acromion forms the summit of the shoulder, and is a large, somewhat triangular or oblong process, flattened from behind forward, projecting at first laterally, and then curving forward and upward, so as to overhang the glenoid cavity.

Figure 3 : Left scapula. Lateral surface.

1. Coracoid process

2. Glenoid cavity

3. Supraspinatous fossa

4. Acromion

5. Infraspinatous fossa

6. Inferior angle

7. Lateral border


Main article: ossification of scapula


The larger part of the scapula undergoes membranous ossification.. Some of the outer parts of the scapula are cartilaginous at birth, and would therefore undergo endochondral ossification .


The head, processes, and the thickened parts of the bone, contain cancellous tissue; the rest consists of a thin layer of compact tissue.


The central part of the supraspinatus fossa and the upper part of the infraspinatous fossa, but especially the former, are usually so thin in humans as to be semitransparent; occasionally the bone is found wanting in this situation, and the adjacent muscles are separated only by fibrous tissue.


Muscular attachments


The following muscles attach to the scapula:






Pectoralis Minor


coracoid process




coracoid process

Serratus Anterior



medial border

Triceps Brachii (long head)



infraglenoid tubercle

Biceps Brachii (short head)



coracoid process

Biceps Brachii (long head)



supraglenoid tubercle




subscapular fossa

Rhomboid Major


medial border

Rhomboid Minor



medial border


Levator Scapulae


medial border




spine of scapula



spine of scapula




supraspinous fossa



infraspinous fossa


Teres Minor


lateral border

Teres Major


lateral border

Latissimus Dorsi (a few fibers)


inferior angle



superior border



Movements of the scapula are brought about by scapular muscles:


Elevation, Depression, Protraction (abduction) Retraction (adduction) Upward (lateral) rotation, Downward (medial) rotation, Anterior Tipping, and Posterior Tipping



Main article: Scapular fracture


Because of its sturdy structure and protected location, scapular fractures are uncommon; when they do occur, they are an indication that severe chest trauma has occurred.


A winged scapula is a condition in which the medial border (the side nearest the spine) of a person's scapula is abnormally positioned outward and backward. The resulting appearance of the upper back is said to be wing-like because the inferior angle of the shoulder blade protrudes backward rather than lying mostly flat. In addition, any condition causing weakness of the serratus anterior muscle may cause scapular "winging".


Shoulder Impingement Syndrome and the Scapula


The scapula has been found to play an important role in shoulder impingement syndrome. It is a wide, flat bone lying on the thoracic wall that provides an attachment for three different groups of muscles. The intrinsic muscles of the scapula include the muscles of the rotator cuff- the subscapularis, teres minor, supraspinatus, and infraspinatus. These muscles attach to the surface of the scapula and are responsible for the internal and external rotation of the glenohumeral joint, along with humeral abduction. The extrinsic muscles include the biceps, triceps, and deltoid muscles and attach to the coracoid process and supraglenoid tubercle of the scapula, infraglenoid tubercle of the scapula, and spine of the scapula. These muscles are responsible for several actions of the glenohumeral joint. The third group, which is mainly responsible for stabilization and rotation of the scapula, consists of the trapezius, serratus anterior, levator scapulae, and rhomboid muscles and attach to the medial, superior, and inferior borders of the scapula. Each of these muscles has their own role in proper shoulder function and must be in balance with each other in order to avoid shoulder pathology. Abnormal scapular function is called scapular dyskinesis. One action the scapula performs during a throwing or serving motion is elevation of the acromion process in order to avoid impingement of the rotator cuff tendons. If the scapula fails to properly elevate the acromion, impingement may occur during the cocking and acceleration phase of an overhead activity. The two muscles most commonly inhibited during this first part of an overhead motion are the serratus anterior and the lower trapezius. These two muscles act as a force couple within the glenohumeral joint to properly elevate the acromion process, and if a muscle imbalance exists, shoulder impingement may develop.


In other animals

Scapulae, spine and ribs of Myotis lucifugus (Little Brown Bat).


In fish, the scapular blade is a structure attached to the upper surface of the articulation of the pectoral fin, and is accompanied by a similar coracoid plate on the lower surface. Although sturdy in cartilagenous fish, both plates are generally small in most other fish, and may be partially cartilagenous, or consist of multiple bony elements.


In the early tetrapods, these two structures respectively became the scapula and a bone referred to as the procoracoid (commonly called simply the "coracoid", but not homologous with the mammalian structure of that name). In amphibians and reptiles (birds included), these two bones are distinct, but together form a single structure bearing many of the muscle attachments for the forelimb. In such animals, the scapula is usually a relatively simple plate, lacking the projections and spine that it possesses in mammals. However, the detailed structure of these bones varies considerably in living groups. For example, in frogs, the procoracoid bones may be braced together at the animal's underside to absorb the shock of landing, while in turtles, the combined structure forms a Y-shape in order to allow the scapula to retain a connection to the clavicle (which is part of the shell). In birds, the procoracoids help to brace the wing against the top of the sternum.


In the fossil therapsids, a third bone, the true coracoid, formed just behind the procoracoid. The resulting three-boned structure is still seen in modern monotremes, but in all other living mammals, the procoracoid has disappeared, and the coracoid bone has fused with the scapula, to become the coracoid process. These changes are associated with the upright gait of mammals, compared with the more sprawling limb arrangement of reptiles and amphibians; the muscles formerly attached to the procoracoid are no longer required. The altered musculature is also responsible for the alteration in the shape of the rest of the scapula; the forward margin of the original bone became the spine and acromion, from which the main shelf of the shoulder blade arises as a new structure.

2) Arm and Forearm (6 bones) - Left and right Humerus (2) (Arm), Ulna (2) and Radius (2) (Fore Arm).

Arm and Forearm (6 bones) - Left and right Humerus (2) (Arm), Ulna (2) and Radius (2) (Fore Arm).

The humerus (pron.: /ˈhjuːmərəs/; ME from Latin humerus, umerus upper arm, shoulder; cf. Gothic ams shoulder, Greek ōmos. Plural: humeri) is a long bone in the arm or forelimb that runs from the shoulder to the elbow.


Anatomically, it connects the scapula and the lower arm (consisting of the radius and ulna), and consists of three sections. The upper extremity consists of a rounded head, a narrow neck, and two short processes (tubercles, sometimes called tuberosities.) Its body is cylindrical in its upper portion, and more prismatic below. The lower extremity consists of 2 epicondyles, 2 processes (trochlea & capitulum), and 3 fossae (radial fossa, coronoid fossa, and olecranon fossa). As well as its true anatomical neck, the constriction below the greater and lesser tubercles of the humerus is referred to as its surgical neck due to its tendency to commonly get fractured, thus often becoming the focus of surgeons.

Position of humerus (shown in red). Anterior view.

Muscles attached to the humerus


The deltoid originates on the lateral third of the clavicle, acromion and the crest of the spine of the scapula. It is inserted on the deltoid tuberosity of the humerus and has several actions including abduction, extension, and circumduction of the shoulder. The supraspinatus also originates on the spine of the scapula. It inserts on the greater tubercle of the humerus, and assists in abduction of the shoulder.


The pectoralis major, teres major, and latissimus dorsi insert at the intertubercular groove of the humerus. They work to adduct and medially, or internally, rotate the humerus.


The infraspinatus and teres minor insert on the greater tubercle, and work to laterally, or externally, rotate the humerus. In contrast, the subscapularis muscle inserts onto the lesser tubercle and works to medially, or internally, rotate the humerus.


The biceps brachii, brachialis, and brachioradialis (which attaches distally) act to flex the elbow. (The biceps, however, does not attach to the humerus.) The triceps brachii and anconeus extend the elbow, and attach to the posterior side of the humerus.



The four muscles of supraspinatus, infraspinatus, teres minor and subscapularis form a musculo-ligamentous girdle called the rotator cuff. This cuff stabilizes the very mobile but inherently unstable glenohumeral joint. The other muscles are used as counterbalances for the actions of lifting/pulling and pressing/pushing.

Left humerus. Anterior view

A. Supraspinatus muscle

B. Latissimus dorsi muscle

C. Pectoralis major muscle

D. Deltoid muscle

E. Brachioradialis

F. Extensor carpi radialis longus muscle


H. Subscapularis muscle

I. Teres major muscle

J. Coracobrachialis muscle

K. Brachialis muscle

L. Pronator teres muscle


Left humerus. Posterior view



At the shoulder, the head of the humerus articulates with the glenoid fossa of the scapula. More distally, at the elbow, the capitulum of the humerus articulates with the head of the radius, and the trochlea of the humerus articulates with the trochlear notch of the ulna.

The left shoulder and acromioclavicular joints, and the proper ligaments of the scapula.

Head of humerus

The Supinator



The axillary nerve is located at the proximal end, against the shoulder girdle. Dislocation of the humerus's glenohumeral joint, has the potential to injure the axillary nerve or the axillary artery. Signs and symptoms of this dislocation include a loss of the normal shoulder contour and a palpable depression under the acromion.


The radial nerve follows the humerus closely. At the midshaft of the humerus, the radial nerve travels from the posterior to the anterior aspect of the bone in the spiral groove. A fracture of the humerus in this region can result in radial nerve injury.


The ulnar nerve at the distal end of the humerus near the elbow is sometimes referred to in popular culture as 'the funny bone'. Striking this nerve can cause a tingling sensation ("funny" feeling), and sometimes a significant amount of pain. It lies anteriorly to the medial epicondyle, and is easily damaged in elbow injuries.

Cross-section through the middle of upper arm.




Human arm bones diagram

Humerus - inferior epiphysis. Anterior view.

Humerus - inferior epiphysis. Posterior view.

Humerus - superior epiphysis.

Ulna: The ulna (/ˈʌlnə/[1][2]) or elbow bone is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position (i.e. when the arms are down at the sides of the body and the palms of the hands face forward) the ulna is located at the side of the forearm closest to the body (the medial side), the side of the little finger.

Upper extremity

Shown is the right hand, palm down (left) and palm up (right). Ulna is #2



The ulna articulates with:

        trochlea of the humerus, at the right side elbow as a hinge joint with semilunar trochlear notch of the ulna.

        the radius, near the elbow as a pivot joint, this allows the radius to cross over the ulna in pronation.

        the distal radius, where it fits into the ulna notch.

        the radius along its length via the interosseous membrane that forms a syndesmoses joint

        it is also called the poisidion

Proximal and distal aspects


The ulna is broader proximally, and narrower distally.


Proximally, the ulna has a bony process, the olecranon process, a hook-like structure that fits into the olecranon fossa of the humerus. This prevents hyperextension and forms a hinge joint with the trochlea of the humerus. There is also a radial notch for the head of the radius, and the ulnar tuberosity to which muscles attach.


At the distal end of the ulna is a styloid process.




The long, narrow medullary cavity is enclosed in a strong wall of compact tissue which is thickest along the interosseous border and dorsal surface. At the extremities the compact layer thins. The compact layer is continued onto the back of the olecranon as a plate of close spongy bone with lamellæ parallel. From the inner surface of this plate and the compact layer below it trabeculæ arch forward toward the olecranon and coronoid and cross other trabeculæ, passing backward over the medullary cavity from the upper part of the shaft below the coronoid. Below the coronoid process there is a small area of compact bone from which trabeculæ curve upward to end obliquely to the surface of the semilunar notch which is coated with a thin layer of compact bone.






Triceps brachii muscle


posterior part of superior surface of Olecranon process (via common tendon)


Anconeus muscle



olecranon process (lateral aspect)

Brachialis muscle


anterior surface of the coronoid process of the ulna

Pronator teres muscle



medial surface on middle portion of coronoid process (also shares origin with medial epicondyle of the humerus)


Flexor carpi ulnaris muscle


olecranon process and posterior surface of ulna (also shares origin with medial epicondyle of the humerus)

Flexor digitorum superficialis muscle



coronoid process (also shares origin with medial epicondyle of the humerus and shaft of the radius)

Flexor digitorum profundus muscle


coronoid process, anteromedial surface of ulna (also shares origin with the interosseous membrane)

Pronator quadratus muscle



distal portion of anterior ulnar shaft


Extensor carpi ulnaris muscle


posterior border of ulna (also shares origin with lateral epicondyle of the humerus)

Supinator muscle



proximal ulna (also shares origin with lateral epicondyle of the humerus)

Abductor pollicis longus muscle



posterior surface of ulna (also shares origin with the posterior surface of the radius bone)

Extensor pollicis longus muscle


dorsal shaft of ulna (also shares origin with the dorsal shaft of the radius and the interosseous membrane)

Extensor pollicis brevis muscle



dorsal shaft of ulna (also shares origin with the dorsal shaft of the radius and the interosseous membrane)

Extensor indicis muscle


posterior surface of distal ulna (also shares origin with the interosseous membrane)



Specific fracture types of the ulna include:

Monteggia fracture - a fracture of the proximal third of the ulna with the dislocation of the head of the radius

Hume fracture - a fracture of the olecranon with an associated anterior dislocation of the radial head

Radius (bone): he radius or radial bone is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna, which exceeds it in length and size. It is a long bone, prism-shaped and slightly curved longitudinally. The radius articulates with the capitulum of the humerus, the radial notch and the head of the ulna. The corresponding bone in the lower leg is the tibia.


The word radius is Latin for "ray". In the context of the radius bone, a ray can be thought of rotating around an axis line extending diagonally from center of capitulum to the center of distal ulna. While the ulna is the major contributor to the elbow joint, the radius primarily contributes to the wrist joint.


The radius is named so because the radius (bone) acts like the radius (of a circle). The ulna acts as the center point to the circle because when the arm is rotated the ulna does not move. The radius (bone) acts like the radius (of a circle) because it rotates around the ulna and the far end (where it joins to the bones of the hand), known as the styloid process of the radius, is the distance from the ulna (center of the circle) to the edge of the radius (the circle).



The radius has a body and two extremities. The upper extremity of the radius consists of a somewhat cylindrical head articulating with the ulna and the humerus, a neck, and a double tuberosity. The body of the radius is self-explanatory, and the lower extremity of the radius is roughly quadrilateral in shape, with articular surfaces for the ulna, scaphoid and lunate bones. The distal end of the radius forms a palpable point called the styloid process. Along with the proximal and distal radioulnar articulations, an interosseous membrane originates medially along the length of the body of the radius to attach the radius to the ulna.

Muscle attachments


The biceps muscle inserts on the radial tuberosity of the upper extremity of the bone. The upper third of the body of the bone attaches to the supinator, the flexor digitorum superficialis, and the flexor pollicis longus muscles. The middle third of the body attaches to the extensor ossis metacarpi pollicis, extensor primi internodii pollicis, and the pronator teres muscles. The lower quarter of the body attaches to the pronator quadratus muscle and the tendon of the supinator longus.




The long narrow medullary cavity is enclosed in a strong wall of compact bone. It is thickest along the interosseous border and thinnest at the extremities, save over the cup-shaped articular surface (fovea) of the head.


The trabeculae of the spongy tissue are somewhat arched at the upper end and pass upward from the compact layer of the shaft to the fovea capituli (the humerus's cup-shaped articulatory notch); they are crossed by others parallel to the surface of the fovea. The arrangement at the lower end is somewhat similar. It is missing in radial aplasia.



A subtle radial head fracture with associated positive sail sign

Radius, styloid process - anterior view

Radius, ulnar noch - posterior veiw


Specific fracture types of the radius include:

Essex-Lopresti fracture - a fracture of the radial head with concomitant dislocation of the distal radio-ulnar joint with disruption of the interosseous membrane.[3]

Distal radius fracture

Galeazzi fracture - a fracture of the radius with dislocation of the distal radioulnar joint

Colles' fracture - a distal fracture of the radius with dorsal (posterior) displacement of the wrist and hand

Smith's fracture - a distal fracture of the radius with volar (ventral) displacement of the wrist and hand

Barton's fracture - an intra-articular fracture of the distal radius with dislocation of the radiocarpal joint.


3) Hands (54 bones) - Left and right Carpal (16) (wrist), Metacarpal (10), Proximal phalanges (10), Middle phalanges (8), distal phalanges (10).

Carpal: In human anatomy, the carpal bones can be classified as belonging to two transverse rows or three longitudinal columns.

Micro-radiography of 8 weeks human embryo hand


Ligaments of the wrist

There are four groups of ligaments in the region of the wrist:

1.     The ligaments of the wrist proper which unite the ulna and radius with the carpus: the ulnar and radial collateral ligaments; the palmar and dorsal radiocarpal ligaments; and the palmar ulnocarpal ligament.

2.     The ligaments of the intercarpal articulations which unite the carpal bones with one another: the radiate carpal ligament; the dorsal, palmar, and interosseous intercarpal ligaments; and the pisohamate ligament,

3.     The ligaments of the carpometacarpal articulations which unite the carpal bones with the metacarpal bones: the pisometacarpal ligament and the palmar and dorsal carpometacarpal ligaments

4.     The ligaments of the intermetacarpal articulations which unite the metacarpal bones: the dorsal, interosseous, and palmar metacarpal ligaments


The pair of rows together form an arch which is convex proximally and concave distally. On the palmar side, the carpus is concave, forming the carpal tunnel which is covered by the flexor retinaculum. Because the proximal row is simultaneously related to the articular surfaces of the radius and the distal row, it adapts constantly to these mobile surfaces. The bones of this row - scaphoid, lunate, and triquetrum - have their individual movements. The scaphoid contributes to the stability of the midcarpus as it articulates distally with the trapezium and the trapezoid. The distal row is more rigid as its transverse arch moves with the metacarpals.


Biomechanically and clinically, the carpal bones are better understood as arranged in three longitudinal columns:

A radial scaphoid column consisting of the scaphoideum, trapezium, and trapezoideum

A lunate column consisting of the lunate and capitate

A ulnar triquetral column consisting of the triquetrum and hamatum.


In this context the pisiform is regarded as a sesamoid bone embedded in the tendon of the flexor carpi ulnaris. The ulnar column leaves a gap between the ulna and the triquetrum, and therefore, only the radial or scaphoid and central or capitate columns articulate with the radius. The wrist is more stable in flexion than in extension more because of the strength of various capsules and ligaments than the interlocking parts of the skeleton.



The hand is said to be in straight position when the third finger runs over the capitate bone and is in a straight line with the forearm. This should not be confused with the midposition of the hand which corresponds to an ulnar deviation of 12 degrees. From the straight position two pairs of movements of the hand are possible: abduction (movement towards the radius, so called radial deviation or abduction) of 15 degrees and adduction (movement towards the ulna, so called ulnar deviation or adduction) of 40 degrees when the arm is in strict supination and slightly greater in strict pronation. Flexion (tilting towards the palm, so called palmar flexion) and extension (tilting towards the back of the hand, so called dorsiflexion) is possible with a total range of 170 degrees.


Radial abduction/ulnar adduction


During radial abduction the scaphoid is tilted towards the palmar side which allows the trapezium and trapezoid to approach the radius. Because the trapezoid is rigidly attached to the second metacarpal bone to which also the flexor carpi radialis and extensor carpi radialis are attached, radial abduction effectively pulls this combined structure towards the radius. During radial abduction the pisiform traverses the greatest path of all carpal bones. Radial abduction is produced by (in order of importance) extensor carpi radialis longus, abductor pollicis longus, extensor pollicis longus, flexor carpi radialis, and flexor pollicis longus.


Ulnar adduction causes a tilting or dorsal shifting of the proximal row of carpal bones. It is produced by extensor carpi ulnaris, flexor carpi ulnaris, extensor digitorum, and extensor digiti minimi.


Both radial abduction and ulnar adduction occurs around a dorsopalmar axis running through the head of the capitate bone.


Palmar flexion/dorsiflexion


During palmar flexion the proximal carpal bones are displaced towards the dorsal side and towards the palmar side during dorsiflexion. While flexion and extension consist of movements around a pair of transverse axes passing through the lunate bone for the proximal row and through the capitate bone for the distal row palmar flexion occurs mainly in the radiocarpal joint and dorsiflexion in the midcarpal joint.


Dorsiflexion is produced by (in order of importance) extensor digitorum, extensor carpi radialis longus, extensor carpi radialis brevis, extensor indicis, extensor pollicis longus, and extensor digiti minimi. Palmar flexion is produced by (in order of importance) flexor digitorum superficialis, flexor digitorum profundus, flexor carpi ulnaris, flexor pollicis longus, flexor carpi radialis, and abductor pollicis longus.


Combined movements


Combined with movements in both the elbow and shoulder joints, intermediate or combined movements in the wrist approximate those of a ball-and-socket joint with some necessary restrictions, such as maximum palmar flexion blocking abduction.


Accessory movements


Anteroposterior gliding movements between adjacent carpal bones or along the midcarpal joint can be achieved by stabilizing individual bones while moving another (i.e. gripping the bone between the thumb and index finger).

Individual bone

Posterior and anterior view of a human carpus



Almost all carpals (except the pisiform) have six surfaces. Of these the palmar or anterior and the dorsal or posterior surfaces are rough, for ligamentous attachment; the dorsal surfaces being the broader, except in the lunate.


The superior or proximal, and inferior or distal surfaces are articular, the superior generally convex, the inferior concave; the medial and lateral surfaces are also articular where they are in contact with contiguous bones, otherwise they are rough and tuberculated.

Metacarpal: In human anatomy, the metacarpus is the intermediate part of the hand skeleton that is located between the phalanges (bones of the fingers) and the carpus which forms the connection to the forearm. The metacarpus consists of metacarpal bones. Its equivalent in the foot is the metatarsus.

The five metacarpal bones, numbered. (Left hand shown with thumb on right.)

Multiple fractures of the metacarpals (aka broken hand). (Right hand shown with thumb on left.)

Human anatomy


The metacarpals form a transverse arch to which the rigid row of distal carpal bones are fixed. The peripheral metacarpals (those of the thumb and little finger) form the sides of the cup of the palmar gutter and as they are brought together they deepen this concavity. The index metacarpal is the most firmly fixed, while the thumb metacarpal articulates with the trapezium and acts independently from the others. The middle metacarpals are tightly united to the carpus by intrinsic interlocking bone elements at their bases. The ring metacarpal forms a transitional element of the semi-independent last metacarpal.


Each metacarpal bone consists of a body and two extremities.




The body (corpus; shaft) is prismoid in form, and curved, so as to be convex in the longitudinal direction behind, concave in front. It presents three surfaces: medial, lateral, and dorsal.

The medial and lateral surfaces are concave, for the attachment of the interosseus muscles, and separated from one another by a prominent anterior ridge.

The dorsal surface presents in its distal two-thirds a smooth, triangular, flattened area which is covered in by the tendons of the extensor muscles. This surface is bounded by two lines, which commence in small tubercles situated on either side of the digital extremity, and, passing upward, converge and meet some distance above the center of the bone and form a ridge which runs along the rest of the dorsal surface to the carpal extremity. This ridge separates two sloping surfaces for the attachment of the interossei dorsales.

To the tubercles on the digital extremities are attached the collateral ligaments of the metacarpophalangeal joints.




The base or carpal extremity (basis) is of a cuboidal form, and broader behind than in front: it articulates with the carpus, and with the adjoining metacarpal bones; its dorsal and volar surfaces are rough, for the attachment of ligaments.




The head or digital extremity (capitulum) presents an oblong surface markedly convex from before backward, less so transversely, and flattened from side to side; it articulates with the proximal phalanx. It is broader, and extends farther upward, on the volar than on the dorsal aspect, and is longer in the antero-posterior than in the transverse diameter. On either side of the head is a tubercle for the attachment of the collateral ligament of the metacarpophalangeal joint.


The dorsal surface, broad and flat, supports the tendons of the extensor muscles.


The volar surface is grooved in the middle line for the passage of the flexor tendons, and marked on either side by an articular eminence continuous with the terminal articular surface.




Besides the metacarpophalangeal joints, the metacarpal bones articulate by carpometacarpal joints as follows:

the first with the trapezium;

the second with the trapezium, trapezoid, capitate and third metacarpal;

the third with the capitate and second and fourth metacarpals;

the fourth with the capitate, hamate, and third and fifth metacarpals;

and the fifth with the hamate and fourth metacarpal.




Extensor Carpi Radialis Longus/Brevis: Both insert on the base of metacarpal II; Assist with wrist extension and radial flexion of the wrist


Extensor Carpi Ulnaris: Inserts on the base of metacarpal V; Extends and fixes wrist when digits are being flexed; assists with ulnar flexion of wrist


Abductor Pollicis Longus: Inserts on the trapezium and base of metacarpal I; Abducts thumb in frontal plane; extends thumb at carpometacarpal joint


Opponens Pollicis: Inserts on metacarpal I; flexes metacarpal I to oppose the thumb to the fingertips


Opponens digiti minimi: Inserts on the medial surface of metacarpal V; Flexes metacarpal V at carpometacarpal joint when little finger is moved into opposition with tip of thumb; deepens palm of hand.


Congenital disorders


The fourth and fifth metacarpal bones are commonly "blunted" or shortened, in pseudohypoparathyroidism and pseudopseudohypoparathyroidism.


A blunted fourth metacarpal, with normal fifth metacarpal, can signify Turner syndrome.


Blunted metacarpals (particularly the fourth metacarpal) are a symptom of Nevoid basal cell carcinoma syndrome.




The neck of a metacarpal (in the transition between the body and the head) is a common location for a boxer's fracture.

Metacarpals of left hand, anterior aspect

Metacarpals of left hand, medial aspect

First metacarpal bone (left)

Second metacarpal bone (left)

Third metacarpal bone (left)

Fourth metacarpal bone (left)

Fifth metacarpal bone (left)


4) Pelvis (2 bones) - Left and right os coxae (2) (ilium).

Pelvis: In human anatomy, the pelvis (plural pelves or pelvises, sometimes also called pelvic region of the trunk) is the lower part of the trunk, between the abdomen and the lower limbs (legs).[1] The pelvis includes several structures:[1]

the bony pelvis, or pelvic skeleton, the part of the skeleton connecting the sacrum region of the spine to the femurs, subdivided into:

        the pelvic girdle (the two hip bones, which are part of the appendicular skeleton) and

        the pelvic region of the spine (sacrum, and coccyx, which are part of the axial skeleton)

        the pelvic cavity, typically defined as a small part of the space enclosed by the pelvic skeleton, delimited by the pelvic brim above and the pelvic floor below; alternatively, the pelvic cavity is sometimes also defined as the whole space enclosed by the pelvic skeleton, subdivided into:

1.     the greater or false pelvis, above the pelvic brim

2.     the lesser or true pelvis, below the pelvic brim

3.     the pelvic floor or pelvic diaphragm, below the pelvic cavity

4.     the perineum, below the pelvic diaphragm


In the human, the pelvic skeleton is formed in the area of the back (posterior dorsal), by the sacrum and the coccyx (the caudal portion of the axial skeleton), and laterally and anteriorly (forward and to the side), by a pair of hip bones, the lower extremity, (parts of the appendicular skeleton). In an adult human being, the pelvic skeleton is thus composed of three large bones, and the coccyx (35 bones); however, before puberty, each hip bone consists of three discrete (separate) bones the ilium, ischium, pubis that have yet to fuse at adulthood; thus, in puberty, the human pelvic skeleton can comprise more than 10 bones, depending upon the composition of the persons coccyx.

Female type pelvis

Male type pelvis

Brief description


The bony pelvis (or pelvic skeleton) is the section between the legs and the torso that connects the spine (backbone) to the thigh bones. In adults, it is mainly constructed of two hip bones, one on the right and one on the left of the body. The two hip bones are each made up of 3 sections, the Ilium, Ischium and Pubis. These sections are fused together during puberty, meaning in childhood they are separate bones. Along with the hip bones is the Sacrum, the upper-middle part of the pelvis, which connects the spine (backbone) to the pelvis. To make this possible, the hip bones are attached to the Sacrum.


The gap enclosed by the pelvic skeleton, called the pelvic cavity, is the section of the body underneath the abdomen and mainly consists of the reproductive organs (sex organs) and the rectum.

Bony pelvis

1. Sacrum

2. Ilium

3. Ischium

4. Pubic bone

5. Pubic symphysis

6. Acetabulum

7. Obturator foramen

8. Coccyx

Red line: Terminal line/pelvic brim




The skeleton of the pelvis is a basin-shaped ring of bones connecting the vertebral column to the femora.


Its primary functions are to bear the weight of the upper body when sitting and standing; transfer that weight from the axial skeleton to the lower appendicular skeleton when standing and walking; and provide attachments for and withstand the forces of the powerful muscles of locomotion and posture. Compared to the shoulder girdle, the pelvic girdle is thus strong and rigid.


Its secondary functions are to contain and protect the pelvic and abdominopelvic viscera (inferior parts of the urinary tracts, internal reproductive organs); provide attachment for external reproductive organs and associated muscles and membranes.


As a mechanical structure


The pelvic girdle consists of the two hip bones. The hip bones are connected to each other anteriorly at the pubic symphysis, and posteriorly to the sacrum at the sacroiliac joints to form the pelvic ring. The ring is very stable and allows very little mobility, a prerequisite for transmitting loads from the trunk to the lower limbs.


As a mechanical structure the pelvis may be thought of as four roughly triangular and twisted rings. Each superior ring is formed by the iliac bone; the anterior side stretches from the acetabulum up to the anterior superior iliac spine; the posterior side reaches from the top of the acetabulum to the sacroiliac joint; and the third side is formed by the palpable iliac crest. The lower ring, formed by the rami of the pubic and ischial bones, supports the acetabulum and is twisted 80-90 degrees in relation to the superior ring.


An alternative approach is to consider the pelvis part of an integrated mechanical system based on the tensegrity icosahedron as an infinite element. Such a system is able to withstand omnidirectional forces ranging from weight-bearing to childbearing and, as a low energy requiring system, is favoured by natural selection.


The pelvic inclination angle is the single most important element of the human body posture and is adjusted at the hips. It is also one of the rare things that can be measured at the assessment of the posture. A simple method of measurement was described by the British orthopedist Philip Willes and is performed by using an inclinometer.



Coronal section through pubic symphysis


The two hip bones are joined anteriorly at the pubic symphysis by a fibrous cartilage covered by a hyaline cartilage, the interpubic disk, within which a non-synovial cavity might be present. Two ligaments, the superior and inferior pubic ligaments, reinforce the symphysis.


Both sacroiliac joints, formed between the auricular surfaces of the sacrum and the two hip bones. are amphiarthroses, almost immobile joints enclosed by very taut joint capsules. This capsule is strengthened by the ventral, interosseous, and dorsal sacroiliac ligaments. The most important accessory ligaments of the sacroiliac joint are the sacrospinous and sacrotuberous ligaments which stabilize the hip bone on the sacrum and prevent the promonotory from tilting forward. Additionally, these two ligaments transform the greater and lesser sciatic notches into the greater and lesser foramina, a pair of important pelvic openings. The iliolumbar ligament is a strong ligament which connects the tip of the transverse process of the fifth lumbar vertebra to the posterior part of the inner lip of the iliac crest. It can be thought of as the lower border of the thoracolumbar fascia and is occasionally accompanied by a smaller ligamentous band passing between the fourth lumbar vertebra and the iliac crest. The lateral lumbosacral ligament is partly continuous with the iliolumbar ligament. It passes between the transverse process of the fifth vertebra to the ala of the sacrum where it intermingle with the anterior sacroiliac ligament.


The joint between the sacrum and the coccyx, the sacrococcygeal symphysis, is strengthened by a series of ligaments. The anterior sacrococcygeal ligament is an extension of the anterior longitudinal ligament (ALL) that run down the anterior side of the vertebral bodies. Its irregular fibers blend with the periosteum. The posterior sacrococcygeal ligament has a deep and a superficial part, the former is a flat band corresponding to the posterior longitudinal ligament (PLL) and the latter corresponds to the ligamenta flava. Several other ligaments complete the foramen of the last sacral nerve.




The lumbosacral joint, between the sacrum and the last lumbar vertebra, has, like all vertebal joints, an intervertebral disc, anterior and posterior ligaments, ligamenta flava, interspinous and supraspinous ligaments, and synovial joints between the articular processes of the two bones. In addition to these ligaments the joint is strengthened by the iliolumbar and lateral lumbosacral ligaments. The iliolumbar ligament passes between the tip of the transverse process of the fifth lumbar vertebra and the posterior part of the iliac crest. The lateral lumbosacral ligament, partly continuous with the iliolumbar ligament, passes down from the lower border of the transverse process of the fifth vertebra to the ala of the sacrum. The movements possible in the lumbosacral joint are flexion and extension, a small amount of lateral flexion (from 7 degrees in childhood to 1 degree in adults), but no axial rotation. Between ages 213 the joint is responsible for as much as 75% (about 18 degrees) of flexion and extension in the lumbar spine. From age 35 the ligaments considerably limit the range of motions.


The three extracapsular ligaments of the hip joint the iliofemoral, ischiofemoral, and pubofemoral ligaments form a twisting mechanism encircling the neck of the femur. When sitting, with the hip joint flexed, these ligaments become lax permitting a high degree of mobility in the joint. When standing, with the hip joint extended, the ligaments get twisted around the femoral neck, pushing the head of the femur firmly into the acetabulum, thus stabilising the joint. The zona orbicularis assists in maintaining the contact in the joint by acting like a buttonhole on the femoral head. The intracapsular ligament, the ligamentum teres, transmits blood vessels that nourish the femoral head.

Pelvic cavity


Main article: Pelvic cavity


The pelvic cavity is a body cavity that is bounded by the bones of the pelvis and which primarily contains reproductive organs and the rectum.


A distinction is made between the lesser or true pelvis inferior to the terminal line, and the greater or false pelvis above it. The pelvic inlet or superior pelvic aperture, which leads into the lesser pelvis, is bordered by the promontory, the arcuate line of ilium, the iliopubic eminence, the pecten of the pubis, and the upper part of the pubic symphysis. The pelvic outlet or inferior pelvic aperture is the region between the subpubic angle or pubic arch, the ischial tuberosities and the coccyx.

Ligaments: obturator membrane, inguinal ligament (lacunar ligament, iliopectineal arch)




Each side of the pelvis is formed as cartilage, which ossifies as three main bones which stay separate through childhood: ilium, ischium, pubis. At birth the whole of the hip joint (the acetabulum area and the top of the femur) is still made of cartilage (but there may be a small piece of bone in the great trochanter of the femur); this makes it difficult to detect congenital hip dislocation by X-raying.



Shoulder and intrinsic back

Intrinsic back muscles


The inferior parts of latissimus dorsi, one of the muscles of the upper limb, arises from the posterior third of the iliac crest. Its action on the shoulder joint are internal rotation, adduction, and retroversion. It also contributes to respiration (i.e. coughing). When the arm is adducted, latissimus dorsi can pull it backward and medially until the back of the hand covers the buttocks.


In a longitudinal osteofibrous canal on either side of the spine there is a group of muscles called the erector spinae which is subdivided into a lateral superficial and a medial deep tract. In the lateral tract, the iliocostalis lumborum and longissimus thoracis originates on the back of the sacrum and the posterior part of the iliac crest. Contracting these muscles bilaterally extends the spine and unilaterally contraction bends the spine to the same side. The medial tract has a "straight" (interspinales, intertransversarii, and spinalis) and an "oblique" (multifidus and semispinalis) component, both of which stretch between vertebral processes; the former acts similar to the muscles of the lateral tract, while the latter function unilaterally as spine extensors and bilaterally as spine rotators. In the medial tract, the multifidi originates on the sacrum.




The muscles of the abdominal wall are subdivided into a superficial and a deep group.


The superficial group is subdivided into a lateral and a medial group. In the medial superficial group, on both sides of the centre of the abdominal wall (the linea alba), the rectus abdominis stretches from the cartilages of ribs V-VII and the sternum down to the pubic crest. At the lower end of the rectus abdominis, the pyramidalis tenses the linea alba. The lateral superficial muscles, the transversus and external and internal oblique muscles, originate on the rib cage and on the pelvis (iliac crest and inguinal ligament) and are attached to the anterior and posterior layers of the sheath of the rectus.


Flexing the trunk (bending forward) is essentially a movement of the rectus muscles, while lateral flexion (bending sideways) is achieved by contracting the obliques together with the quadratus lumborum and intrinsic back muscles. Lateral rotation (rotating either the trunk or the pelvis sideways) is achieved by contracting the internal oblique on one side and the external oblique on the other. The transversus' main function is to produce abdominal pressure in order to constrict the abdominal cavity and pull the diaphragm upward.


There are two muscles in the deep or posterior group. Quadratus lumborum arises from the posterior part of the iliac crest and extends to the rib XII and lumbar vertebrae I-IV. It unilaterally bends the trunk to the side and bilaterally pulls the 12th rib down and assists in expiration. The iliopsoas consists of psoas major (and occasionally psoas minor) and iliacus, muscles with separate origins but a common insertion on the lesser trochanter of the femur. Of these, only iliacus is attached to the pelvis (the iliac fossa). However, psoas passes through the pelvis and because it acts on two joints, it is topographically classified as a posterior abdominal muscle but functionally as a hip muscle. Iliopsoas flexes and externally rotates the hip joints, while unilateral contraction bends the trunk laterally and bilateral contraction raises the trunk from the supine position.


Pelvic floor



The pelvic floor has two inherently conflicting functions: One is to close the pelvic and abdominal cavities and bear the load of the visceral organs, the other is to control the openings of the rectum and urogenital organs that pierce the pelvic floor and make it weaker. To achieve both these tasks, the pelvic floor is composed of several overlapping sheets of muscles and connective tissues.


The pelvic diaphragm is composed of the levator ani and the coccygeus muscle. These arise between the symphysis and the ischial spine and converge on the coccyx and the anococcygeal ligament which spans between the tip of the coccyx and the anal hiatus. This leaves a slit for the anal and urogenital openings. Because of the width of the genital aperture, which is wider in females, a second closing mechanism is required. The urogenital diaphragm consists mainly of the deep transverse perineal which arises from the inferior ischial and pubic rami and extends to the urogential hiatus. The urogenital diaphragm is reinforced posteriorly by the superficial transverse perineal.


The external anal and urethral sphincters close the anus and the urethra. The former is surrounded by the bulbospongiosus which narrows the vaginal introitus in females and surrounds the corpus spongiosum in males. Ischiocavernosus squeezes blood into the corpus cavernosum penis and clitoridis.


Hip and thigh

Muscles of the hip


The muscles of the hip are divided into a dorsal and a ventral group.


The dorsal hip muscles are either inserted into the region of the lesser trochanter (anterior or inner group) or the greater trochanter (posterior or outer group). Anteriorly, the psoas major (and occasionally psoas minor) originates along the spine between the rib cage and pelvis. The iliacus originates on the iliac fossa to join psoas at the iliopubic eminence to form the iliopsoas which is inserted into the lesser trochanter. The iliopsoas is the most powerful hip flexor.


The posterior group includes the gluteii maximus, medius, and minimus. Maximus has a wide origin stretching from the posterior part of the iliac crest and along the sacrum and coccyx, and has two separate insertions: a proximal which radiates into the iliotibial tract and a distal which inserts into the gluteal tuberosity on the posterior side of the femoral shaft. It is primarily an extensor and lateral rotator of the hip joint, but, because of its bipartite insertion, it can both adduct and abduct the hip. Medius and minimus arise on the external surface of the ilium and are both inserted into the greater trochanter. Their anterior fibers are medial rotators and flexors while the posterior fibers are lateral rotators and extensors. The piriformis has its origin on the ventral side of the sacrum and is inserted on the greater trochanter. It abducts and laterally rotates the hip in the upright posture and assists in extension of the thigh. The tensor fasciae latae arises on the anterior superior iliac spine and inserts into the iliotibial tract. It presses the head of the femur into the acetabulum and flexes, medially rotates, and abducts the hip.


The ventral hip muscles are important in the control of the body's balance. The internal and external obturator muscles together with the quadratus femoris are lateral rotators of the hip. Together they are stronger than the medial rotators and therefore the feet point outward in the normal position to achieve a better support. The obturators have their origins on either sides of the obturator foramen and are inserted into the trochanteric fossa on the femur. Quadratus arises on the ischial tuberosity and is inserted into the intertrochanteric crest. The superior and inferior gemelli, arising from the ischial spine and ischial tuberosity respectively, can be thought of as marginal heads of the obturator internus, and their main function is to assist this muscle.

Anterior thigh muscles

Posterior thigh muscles


The muscles of the thigh can be subdivided into adductors (medial group), extensors (anterior group), and flexors (posterior group). The extensors and flexors act on the knee joint, while the adductors mainly act on the hip joint.


The thigh adductors have their origins on the inferior ramus of the pubic bone and are, with the exception of gracilis, inserted along the femoral shaft. Together with sartorius and semitendinosus, gracilis reaches beyond the knee to their common insertion on the tibia.


The anterior thigh muscles form the quadriceps which is inserted on the patella with a common tendon. Three of the four muscles have their origins on the femur, while rectus femoris arises from the anterior inferior iliac spine and is thus the only of the four acting on two joints.


The posterior thigh muscles have their origins on the inferior ischial ramus, with the exception of the short head of the biceps femoris. The semitendinosus and semimembranosus are inserted on the tibia on the medial side of the knee, while biceps femoris is inserted on the fibula, on the knee's lateral side.


Pregnancy and childbirth


In later stages of pregnancy the fetus's head aligns inside the pelvis. Also joints of bones soften due to the effect of pregnancy hormones. These factors may cause pelvic joint pain (Symphysis Pubis Dysfunction or SPD). As the end of pregnancy approaches, the ligaments of the sacroiliac joint loosen, letting the pelvis outlet widen somewhat; this is easily noticeable in the cow.


During childbirth (unless by Cesarean section) the fetus passes through the maternal pelvic opening.


Sexual dimorphism


Modern humans are to a large extent characterized by bipedal locomotion and large brains. Because the pelvis is vital to both locomotion and childbirth, natural selection has been confronted by two conflicting demands: a wide birth canal and locomotion efficiency, a conflict referred to as the "obstetrical dilemma". The female pelvis has evolved to its maximum width for childbirth a wider pelvis would make women unable to walk. In contrast, human male pelves are not constrained by the need to give birth and therefore are optimized for bipedal locomotion.


The principal differences between male and female true and false pelvis include:

The female pelvis is larger and broader than the male pelvis which is taller, narrower, and more compact.

The female inlet is larger and oval in shape, while the male sacral promontory projects further (i.e. the male inlet is more heart-shaped).

The sides of the male pelvis converge from the inlet to the outlet, whereas the sides of the female pelvis are wider apart.

The angle between the inferior pubic rami is acute (70 degrees) in men, but obtuse (90-100 degrees) in women. Accordingly, the angle is called subpubic angle in men and pubic arch in women. Additionally, the bones forming the angle/arch are more concave in females but straight in males.

The distance between the ischia bones is small in males, making the outlet narrow, but large in females, who have a relatively large outlet. The ischial spines and tuberosities are heavier and project farther into the pelvic cavity in males. The greater sciatic notch is wider in females.

The iliac crests are higher and more pronounced in males, making the male false pelvis deeper and more narrow than in females.

The male sacrum is long, narrow, more straight, and has a pronounced sacral promontory. The female sacrum is shorter, wider, more curved posteriorly, and has a less pronounced promontory.

The acetabula are wider apart in females than in males. In males, the acetabulum faces more laterally, while it faces more anteriorly in females. Consequently, when men walk the leg can move forwards and backwards in a single plane. In women, the leg must swing forward and inward, from where the pivoting head of the femur moves the leg back in another plane. This change in the angle of the femoral head gives the female gait its characteristic (i.e. swinging of hips).

See also: Sex differences in humans


Caldwell-Moloy classification


Throughout the 20th century pelvimetric measurements were made on pregnant women to determine whether a natural birth would be possible, a practice today limited to cases where a specific problem is suspected or following a caesarean delivery. William Edgar Caldwell and Howard Carmen Moloy studied collections of skeletal pelves and thousands of stereoscopic radiograms and finally recognized three types of female pelves plus the masculine type. In 1933 and 1934 they published their typology, including the Greek names since then frequently quoted in various handbooks: Gynaecoid (gyne, woman), anthropoid (anthropos, human being), platypelloid (platys, flat), and android (aner, man).

The gynaecoid pelvis is the so-called normal female pelvis. Its inlet is either slightly oval, with a greater transverse diameter, or round. The interior walls are straight, the subpubic arch wide, the sacrum shows an average to backward inclination, and the greater sciatic notch is well rounded. Because this type is spacious and well proportioned there is little or no difficulty in the birth process. Caldwell and his co-workers found gynaecoid pelves in about 50 per cent of specimens.

The platypelloid pelvis has a transversally wide, flattened shape, is wide anteriorly, greater sciatic notches of male type, and has a short sacrum that curves inwards reducing the diameters of the lower pelvis. This is similar to the rachitic pelvis where the softened bones widen laterally because of the weight from the upper body resulting in a reduced anteroposterior diameter. Giving birth with this type of pelvis is associated with problems, such as transverse arrest. Less than 3 per cent of women have this pelvis type.

The android pelvis is a female pelvis with masculine features, including a wedge or heart shaped inlet caused by a prominent sacrum and a triangular anterior segment. The reduced pelvis outlet often causes problems during child birth. In 1939 Caldwell found this type in one third of white women and in one sixth of non-white women.

The anthropoid pelvis is characterized by an oval shape with a greater anteroposterior diameter. It has straight walls, a small subpubic arch, and large sacrosciatic notches. The sciatic spines are placed widely apart and the sacrum is usually straight resulting in deep non-obstructed pelvis. Caldwell found this type in one quarter of white women and almost half of non-white women.


However, Caldwell and Moloy then complicated this simple fourfold scheme by dividing the pelvic inlet into posterior and anterior segments. They named a pelvis according to the anterior segment and affixed another type according to the character of the posterior segment (i.e. anthropoid-android) and ended up with no less than 14 morphologies. Notwithstanding the popularity of this simple classification, the pelvis is much more complicated than this as the pelvis can have different dimensions at various levels of the birth canal.


Caldwell and Moloy also classified the physique of women according to their types of pelves: the gynaecoid type has small shoulders, a small waist and wide hips; the android type looks square-shaped from behind; and the anthropoid type has wide shoulders and narrow hips. Lastly, in their article they described all non-gynaecoid or "mixed" types of pelves as "abnormal", a word which has stuck in the medical world even though at least 50 per cent of women have these "abnormal" pelves.


The classification of Caldwell and Moloy was influenced by earlier classifications attempting to define the ideal female pelvis, treating any deviations from this ideal as dysfunctions and the cause of obstructed labour. In the 19th century anthropologists and others saw an evolutionary scheme in these pelvic typologies, a scheme since then refuted by archaeology. Since the 1950s malnutrition is thought to be one of the chief factors affecting pelvic shape in the Third World even though there are at least some genetic component to variation in pelvic morphology.


Nowadays obstetric suitability of the female pelvis is assessed by ultrasound. The dimensions of the head of the fetus and of the birth canal are accurately measured and compared, and the feasibility of labor can be predicted.


5) Thigh and leg (8 bones) - Femur (2) (thigh), Tibia (2), Patella (2) (knee), and Fibula (2) (leg).


6) Feet and ankles (52 bones) - Tarsals (14) (ankle), Metatarsals (10), Proximal phalanges (10), middle phalanges (8), distal phalanges (10).


It is important to realize that through anatomical variation it is common for the skeleton to have many extra bones (sutural bones in the skull, cervical ribs, lumbar ribs and even extra lumbar vertebrae)


The appendicular skeleton of 126 bones and the axial skeleton of 80 bones together form the complete skeleton of 206 bones in the human body. Unlike the axial skeleton, the appendicular skeleton is unfused. This allows for a much greater range of motion.

Appendicular skeleton diagram



The Skeletal System


Muscular system

The muscular system is the biological system of humans that allows them to move. The muscular system in vertebrates is controlled through the nervous system, although some muscles (such as the cardiac muscle) can be completely autonomous.

Skeletal muscle structure

Skeletal muscle fibers are multinucleated, with the cell's nuclei located just beneath the plasma membrane. The cell is comprised of a series of striped or striated, thread-like myofibrils. Within each myofibril there are protein filaments that are anchored by dark Z lines. The fiber is one long continuous thread-like structure. The smallest cross section of skeletal muscle is called a sarcomere which is the functional unit within the cell. It extends from one Z line to the next attached Z line. The individual sarcomere has alternating thick myosin and thin actin protein filaments. Myosin forms the center or middle of each sarcomere. The exact center of the sarcomere is designated the M line. Thinner actin filaments form a zig zag pattern along the anchor points or Z line.

Upon stimulation by an action potential, skeletal muscles perform a coordinated contraction by shortening each sarcomere. The best proposed model for understanding contraction is the sliding filament model of muscle contraction. Actin and myosin fibers overlap in a contractile motion towards each other. Myosin filaments have club-shaped heads that project toward the actin filaments.

Larger structures along the myosin filament called myosin heads are used to provide attachment points on binding sites for the actin filaments. The myosin heads move in a coordinated style, they swivel toward the center of the sarcomere, detach and then reattach to the nearest active site of the actin filament. This is called a rachet type drive system. This process consumes large amounts of adenosine triphosphate (ATP).

Energy for this comes from ATP, the energy source of the cell. ATP binds to the cross bridges between myosin heads and actin filaments. The release of energy powers the swiveling of the myosin head. Muscles store little ATP and so must continuously recycle the discharged adenosine diphosphate molecule (ADP) into ATP rapidly. Muscle tissue also contains a stored supply of a fast acting recharge chemical, creatine phosphate which can assist initially producing the rapid regeneration of ADP into ATP.

Calcium ions are required for each cycle of the sarcomere. Calcium is released from the sarcoplasmic reticulum into the sarcomere when a muscle is stimulated to contract. This calcium uncovers the actin binding sites. When the muscle no longer needs to contract, the calcium ions are pumped from the sarcomere and back into storage in the sarcoplasmic reticulum.

Control of muscle contraction

Neuromuscular junctions are the focal point where a motor neuron attaches to a muscle. Acetylcholine, (a neurotransmitter used in skeletal muscle contraction) is released from the axon terminal of the nerve cell when an action potential reaches the miscoscopic junction, called a synapse. A group of chemical messengers cross the synapse and stimulate the formation of electrical changes, which are produced in the muscle cell when the acetylcholine binds to receptors on its surface. Calcium is released from its storage area in the cell's sarcoplasmic reticulum. An impulse from a nerve cell causes calcium release and brings about a single, short muscle contraction called a muscle twitch. If there is a problem at the neuromuscular junction, a very prolonged contraction may occur, tetanus. Also, a loss of function at the junction can produce paralysis.

Skeletal muscles are organized into hundreds of motor units, each of which involves a motor neuron, attached by a series of thin finger-like structures called axon terminals. These attach to and control discrete bundles of muscle fibers. A coordinated and fine tuned response to a specific circumstance will involve controlling the precise number of motor units used. While individual muscle units contract as a unit, the entire muscle can contract on a predetermined basis due to the structure of the motor unit. Motor unit coordination, balance, and control frequently come under the direction of the cerebellum of the brain. This allows for complex muscular coordination with little conscious effort, such as when one drives a car without thinking about the process.


Muscle activity in an anaerobic vs aerobic environment

Some information in this article or section has not been verified and may not be reliable.
Please check for inaccuracies, and modify and cite sources as needed.

At rest, the body produces small amounts of ATP in an anaerobic production model through glycolysis in the cytoplasm of muscle cells. As activity increases to a sustained higher activity level such as in running, the body can shift to aerobic ATP production by producing increases in respiratory rate and heart rate. This allows for a greater supply of oxygen to stimulate aerobic production of ATP which occurs in the mitochondria. Once the activity levels decrease, such as occurs at the end of a race, the body will continue to maintain a short elevated respiratory and heart rate while the energy borrowed from the bone cells during the transformation to the aerobic mode is restored. This physiological process is called repayment of oxygen debt. Once all borrowed substances have been repaid to the muscle cells, the body will return to homestatic metabolism.


Skeleton Crossword Puzzlehttp://www.roqa.co.uk/assets/images/skeleton.gif

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Bones Word Search

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4. Hansen J. T. Netters Anatomy Coloring Book. Saunders Elsevier, 2010. 121 p.

5. Henderson B., Dorsey J. L. Medical Terminology for Dummies. Willey Publishing, 2009. P. 189-211.