Human Bones

The bones form the skeletal system. The skeleton actually is of two types; exoskeleton and endoskeleton. Humans don't have exoskeleton. Instead, we have epithelial system including skin, nails and hair.
The human skeleton is studied in two parts; (1) Axial skeletal system (2) Appendicular skeletal system.

(1) The axial skeletal system: The bones of body excluding hands and legs (technically, upper and lower limbs) and the bones involved in their joints to rest of the body (the girdles). Axial skeletal system is basically everything surrounding the medial line of the body. It is again divided into following parts:

 (a) Skull: Skull or head comprises of Cranium, Bones of ears and other facial bones. Sometimes, hyoid bone is also counted in the head itself. But I personally treat it as a seperate bone.
(i) Cranium: It consist of 1 frontal bone (forehead), 2 parietal bones (both sides of frontal), 2 temporal bones (till ears), 1 occipital bone (covering cerebellum, at the back), 1 sphenoid bone (hidden) and 1 ethmoid bone (hidden).
(ii) Bones of ears: Ears have 1 malleus each (also known as hammer bone), 1 incus each (also known as anvil bone) and 1 stapes (also known as stirrup bone, the smallest bone of the body). Thus making total 6 bones in ears.
(iii) Other facial bones: There is 1 mandible (lower jaw), 2 bones of maxilla (upper jaw) one each side, two paletine bones (on palate of oral cavity), 2 zygomatic bones (forming cheeks), 2 nasal bones, 2 lacrimal bones (behind nose), 2 inferior nasal conchae (in inner nasal cavity) and 1 vomer bone (hidden).
(iv) Hyoid bone: This is the only bone in the entire human body which is not articulated (connected with other bones) at all. It freely suspends with the help of muscles in throat.

(b) Vertebrae: It is also called as backbone. This is a misnomer because backbone is not a single bone. It is made up of five types of bones.
(i) Cervical: 7 in number. The topmost bone is known as atlas. The skull rotates on the atlas bone. The second cervical bone is axis. The The atlas gets fit on it. When a person is hanged, the shock of sudden pressure of rope on neck cause this socket of atlas and axis and axis gets through the spinal cord causing immediate death.
(ii) Thoracic: They are 12. 'Thoracic' word comes from thorax. These bones are just behind the chest.
(iii) Lumbar: They are 5 in number. They extend from bottom of chest to top of pelvis. Usually, for surgery below waist, doctors give the injection of anasthesia in lumbar region spinal cord.
(iv) Sacral: Initially, these bones used to be 5 in number before infancy, but with course of time, they fuse and form one sacrum bone.
(v) Coccyx: Also known as coccygeal bone, it is also a bone resulted as fusion of bones, just like sacrum.

(c) Sternum: It is known as chest bone. It is fusion of three bones, (i) Manubrum (top most), (ii) Gladiolus (middle and body of sternum) and (iii) Xiphoid process (bottom most).

(d) The rib-cage: The ribs are of 3 types: (i) true ribs, that connect the vertebra to sternum half way themselves, and remaining through cartillage. They are 7 pairs (total 14) (ii) False ribs, those do not join to sternum, but join to immediately previous rib to them. They are 3 pairs (total 6) (iii) Floating ribs, those do not connect to anything in ventral side at all but remain connected to vertebra in dorsal side. They are 2 pairs i.e. total 4. Hence, ribs are 24 in total.

(2) The appendicular skeletal system: This comprises of four parts. Two types of girdles and 2 types of limbs.

(a) The forelimbs: Hands make the forelimbs. It has 30 bones in each hand. 1 humerous (upper arm), 1 radius and 1 ulna (both in lower arm), 8 carpals (wrist bones), 5 metacarpals and 14 phalanges (3 in each finger and 2 in thumb).

(b) The hindlimbs: Technically, leg is just the lower part of the hindlimb. Each hindlimb also has 30 bones. Classification is as follows; 1 femur (the longest bone in body, present in thigh), 1 tibia and 1 ulna (both in leg), 7 tarsals (similar to 8 carpals in hand), 5 metatarsals (similar to 5 metacarpals in hand), 14 phalanges (similar to 14 phalanges in hand). The remaining one bone (short in tarsals, if compared with carpals) is the patella (also known as knee cap). Biologists believe that once upon a time, this bone also used to be a tarsal but with evolution, it merged out to be patella.

(c) The pelvic girdle: It connects the hindlimbs with the axial skeleton. It comprises of three bones namely ilium, ischium and pubis. Besides these bones, there is special importance of the acetabulum, the cavity for attachment of femur ot pelvis. Some anatomists consider the sacrum and coccyx in pelvic girdle rather than in vertebral column.

(d) The pectoral girdle: It connects the forelimbs with axial skeleton. It has two bones namely clavicle (collar bone) and scapula (shoulder blade). The analogous structure to acetabulum in pectoral girdle is glenoid cavity.

Tech Fact : Study of bones is known as osteology. Study of cartillage os known as chodriology.


Tech Fact : The proximal parts of long bones are seat of RBC formation. Usually, the bone marrow sample for medical-tests is taken from the iliac crest as it is closer to surface.
Tech Fact : Teeth are not counted among bones.
Tech Fact : Skeleton is the only portion left over when a cadaver is allowed to decompose under naturally circumstances. But cartillage decompose unlike bones.
Tech Fact : Bones are not dead. They need continuous blood supply to keep its cells remain alive. The tissues in bones are classified among connective tissues.