Page:Structure and functions of the body; a hand-book of anatomy and physiology for nurses and others desiring a practical knowledge of the subject (IA structurefunctio00fiskrich).pdf/198

 leg on the thigh, but where the biceps rotates the leg out they, being attached to the inner side of the leg bones, rotate it in.

The patella, or small pan, is a flat, somewhat triangular bone developed in the quadriceps extensor tendon. Four muscles are attached to it as well as the ligamentum patellæ, which holds it to the tibia and gives increased leverage by making the quadriceps extensor work at a greater angle. It articulates with the condyles and serves to protect the joint. One bursa, the ''prepatella bursa'', separates it from the skin and another, surrounded by adipose tissue, from the head of the tibia. The external surface can be seen and felt on the front of the knee and the bone can be moved from side to side when the leg is straight.

Joints of the Lower Extremity.—The hip-joint is a ball-and-socket joint but is not so freely movable as the shoulder-joint, the head of the femur being held in the acetabulum by many strong ligaments, of which the most important is the capsular ligament.

The knee-joint is largely a hinge-joint, but in some positions it has some rotation. It is formed by the condyles of the femur, the head of the tibia, and the patella, and has fourteen ligaments, including the ''ligamentum patellæ and the crucial ligaments''. Its synovial sac is the largest found in any joint. Two ''semilunar cartilages'', placed on the head of the tibia, serve to deepen the socket for the condyles, changing somewhat in shape and thickness as the joint moves. The interval between the thigh and the leg bones can be felt at the knee. When the leg is extended the juncture of the bones is slightly above the patella, while in flexion a knife passed below the apex of the patella will pass into the joint.

Congenital dislocation of the hip occurs. Separation of the epiphysis of the femur may occur and sometimes the neck, rarely the lower part of the shaft, is fractured. Either condyle may be fractured off or there may be a T-fracture, in which case the popliteal artery may be