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Before birth a skeleton of cartilage supports human body, but by the time of birth much of the cartilage had been transformed into 350 bones. As one grows many of these bones fuse with one another so that at adult stage, skeleton consists of 206 bones that are grouped into two divisions. These divisions of the bones of human beings are axial skeleton and the appendicular skeleton. Axial skeleton is the basic framework around which the body is built and the appendicular skeleton comprises of the extremities of the body.
Axial skeleton in the human body consists of skull, vertebrae and ribs. Appendicular skeleton of the human body includes the pectoral girdle with fore limbs and pelvic girdle and the hind limbs.
As described earlier, the axial skeleton consists of skull, vertebrae and ribs. It is the basic framework around which the body is built.
Skull: The skull consists of cranium, face or facial bone, ear bone or auditory bones and hyoid bone. The primary function of the skull is the protection of the brain that lies inside it. The human skull is composed of 22 bones besides 6 tiny auditory ossicles and one hyoid bone. At the time of the birth several of the bones of the cranium are not completely formed. If the bones of cranium were completely formed at the time of birth, great difficulty would have been experienced during birth in the birth canal.
Vertebral column: The vertebral column forms more or less a rigid rod. It extends through the length of the trunk on the dorsal side and forms the backbone. It houses and protects the spinal cord. It is a place of attachment of pelvic and pectoral girdle.
In man there are 33 vertebrae. Seven out of these 33 are cervical lying in the neck region, 12 are thoracic vertebrae lying in the thorax, 5 are lumbar vertebrae lying in the lower back region, 5 are sacral vertebrae lying in the sacral region and at the end of the vertebral column is the coccyx or tail bone consisting of 4 small fused vertebrae. The coccyx is the man’s vestige of tail.
Ribs: In man there are twelve pairs of ribs, one pair articulating with each of the thoracic vertebra forming a cage that encloses the heart and the lungs. Ten pairs out of the total 12 pairs of ribs are connected anteriorly with the sternum. Seven pairs out of these 10 pairs are directly connected with the sternum and are known as true ribs. The remaining three pairs are connected with the sternum through costal arch and are known as false ribs. The lower two pairs of ribs are not attached in front and are known as the floating ribs.
The appendicular skeleton consists of pectoral girdles with forelimbs and the pelvic girdles with the hind limbs.
Pectoral girdle: The bones of the pectoral girdle consist of the scapula and the clavicle.
Upper limbs: The upper limbs consists of a humerus in the upper arm region, a radius and ulna in the lower arm region, 8 carpals in the wrist region and 5 metacarpals in the palm of the hand and 14 phalanges.
Pelvic girdle: Hind limbs are attached to the vertebral column through the pelvic girdle which is made up of two hip bones. Each of these bones is formed by the combination of three bones; ischium, illium and pubis.
Lower limbs: In the lower limb there is a single femur in the thigh, tibia and fibula in the shank, 8 ankle bones followed by five longer metatarsals and finally five rows of fourteen phalanges in the toe.