192 THE LOWER EXTREMITIES. 



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 

 patellae, 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 ex- 

 ternal 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 con- 

 dyles of the femur, the head of the tibia, and the patella, 

 and has fourteen ligaments, including the ligamentum 

 patella? 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 



