Human Skeleton :
Human endoskeleton is divided into two parts namely Axial skeleton and Appendicular skeleton.
A) Axial skeleton -
Axial skeleton consists of 80 bones. It consists of Skull, Hyoid bone, Vertebral column and Thoracic cage.
The skull is formed by 28 bones. Human skull is dicondylar (presence of two occipital condyles at the base of skull), immovable except the mandible which is movable. It shows main parts like - Cranium, Face, Ear ossicles. Skull protect the brain and provides sockets for ear, nasal chamber and eyes. The skull gives proper shape to the head and face. Mandible bone helps in opening and closing of the mouth.
Vertebral Column :
It is also called backbone or spine. It forms the central axis of the body. Human vertebral column consists of a chain of 33 small ring like bones called vertebrae. In adult, 5 sacral vertebrae fuse to form a sacrum bone and 4 coccygeal vertebrae fused to form a coccyx bone. Thus, vertebral column consists of 26 bones.
According to the position, the vertebral column consists of - 7 cervical vertebrae, 12 thoracic vertebrae, 5 lumber vertebrae, 5 Sacral vertebrae (fused in adult to form a sacrum) and 4 coccygeal vertebrae (fused in adult to form a coccyx).
Human vertebral column shows four curvatures - Cervical, Thoracic, Lumbar and Sacral. The cervical and lumber curvatures are directed forward while the thoracic and sacral curvatures are directed backward. The curvatures primarily help to balance the erect posture of body.
Thoracic cage :
The thoracic cage is formed by 12 thoracic vertebrae, 12 pairs of ribs and a sternum. Ribs are articulated dorsally with 12 thoracic vertebrae and ventrally with sternum. The last two pairs of ribs are called floating ribs. Sternum (breast bone) is a long and flat bone. In adult, it measures about 15 to 17 cm in length. It is present in mid-ventral region. It is divided into three parts - Manubrium, Body and Xiphoid process. Thoracic cage gives proper shape to the thorax. It helps in breathing movements along with muscular diaphragm and intercostal muscles.
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| Entire human skeleton (Anterior view) |
B) Appendicular skeleton:
It consists of 126 bones. It includes the bones of girdle and bones of limbs. Pectoral girdle is made up of two symmetrical halves. Each half consists of two bones, scapula and clavicle. Pelvic girdle consists of two large hip bones (innominate bones or coxal bones). which are articulated anteriorly in mid line by cartilagenous joint called pubic symphysis. Each hipbone is formed by the ossification of ilium, pubis and ischium and hence also called os-innominate / os-coxal.
Each forelimb consists of 30 bones. It consists of bones, such as Humerus, Radius-ulna and Bones of Hand. Each hind limb consists of 30 bones. It consists of - Femur, Tibia fibula and foot bones.