In a normal hip, the smooth, rounded head of the femur fits deeply and snugly into the acetabulum. (dogtime.com)
The hip is a ball - and - socket joint: the ball is the round head of the femur (thighbone) and the acetabulum (socket) is the concave indentation of the pelvis. (dogtime.com)
They originate at your lumbar spine (lower back) and attach to the inner head of your femur or thigh bone. (weckmethod.com)