hip

The hip is the joint between the thighbone (femur) and the pelvis. It is a ball-and-socket joint; the round head of the femur rests in a cavity (the acetabulum) that allows the leg to rotate freely. In amphibians and reptiles, the femur extends horizontally, and the pelvic girdle is relatively weak. As a result, their trunks often rest partly on the ground, unable to resist gravity effectively. Mammals have hip joints that permit the femur to drop vertically, allowing them to hold themselves off the ground and lead to running and leaping specializations. Related: Pelvic girdle.

You May Also Like!