THE POSTERIOR FEMORAL MUSCLES 479 



impression on the back part of the tuberosity of the ischium, by a tendon common 

 to it and the Semitendinosus, and from the lower part of the sacrotuberous liga- 

 ment; the other, the short head, arises from the lateral lip of the linea aspera, 

 between the Adductor magnus and Vastus lateralis, extending up almost as high 

 as the insertion of the Glutseus maximus; from the lateral prolongation of the 

 linea aspera to within 5 cm. of the lateral condyle; and from the lateral inter- 

 muscular septum. The fibers of the long head form a fusiform belly, which passes 

 obliquely downward and lateralward across the sciatic nerve to end in an aponeu- 

 rosis which covers the posterior surface of the muscle, and receives the fibers of 

 the short head; this aponeurosis becomes gradually contracted into a tendon, 

 which is inserted into the lateral side of the head of the fibula, and by a small 

 slip into the lateral condyle of the tibia. At its insertion the tendon divides into 

 two portions, which embrace the fibular collateral ligament of the knee-joint. 

 From the posterior border of the tendon a thin expansion is given off to the fascia 

 of the leg. The tendon of insertion of this muscle forms the lateral hamstring; 

 the common peroneal nerve descends along its medial border. 



Variations. The short head may be absent; additional heads may arise from the ischial 

 tuberosity, the linea aspera, the medial supracondylar ridge of the femur or from various other 

 parts. A slip may pass to the Gastrocnemius. 



The Semitendinosus, remarkable for the great length of its tendon of insertion, 

 is situated at the posterior and medial aspect of the thigh. It arises from the lower 

 and medial impression on the tuberosity of the ischium, by a tendon common 

 to it and the long head of the Biceps femoris; it also arises from an aponeurosis 

 which connects the adjacent surfaces of the two muscles to the extent of about 

 7.5 cm. from their origin. The muscle is fusiform and ends a little below the middle 

 of the thigh in a long round tendon which lies along the medial side of the popliteal 

 fossa; it then curves around the medial condyle of the tibia and passes over the 

 tibial collateral ligament of the knee-joint, from which it is separated by a bursa, 

 and is inserted into the upper part of the medial surface of the body of the tibia, 

 nearly as far forward as its anterior crest. At its insertion it gives off from its 

 lower border a prolongation to the deep fascia of the leg and lies behind the tendon 

 of the Sartorius, and below that of the Gracilis, to which it is united. A tendinous 

 intersection is usually observed about the middle of the muscle. 



The Semimembranosus, so called from its membranous tendon of origin, is situ- 

 ated at the back and medial side of the thigh. It arises by a thick tendon from 

 the upper and outer impression on the tuberosity of the ischium, above and lateral 

 to the Biceps femoris and Semitendinosus. The tendon of origin expands into an 

 aponeurosis, which covers the upper part of the anterior surface of the muscle; from 

 this aponeurosis muscular fibers arise, and converge to another aponeurosis which 

 covers the lower part of the posterior surface of the muscle and contracts into the 

 tendon of insertion. It is inserted mainly into the horizontal groove on the posterior 

 medial aspect of the medial condyle of the tibia. The tendon of insertion gives off 

 certain fibrous expansions : one, of considerable size, passes upward and lateralward 

 to be inserted into the back part of the lateral condyle of the femur, forming part 

 of the oblique popliteal ligament of the knee-joint ; a second is continued downward 

 to the fascia which covers the Popliteus muscle; while a few fibers join the tibial 

 collateral ligament of the joint and the fascia of the leg. The muscle overlaps the 

 upper part of the popliteal vessels. 



Variations. It may be reduced or absent, or double, arising mainly from the sacrotuberous 

 ligament and giving a slip to the femur or Adductor magnus. 



The tendons of insertion of the two preceding muscles form the medial ham- 

 strings. 



