ENDOSKELETON AND VOLUNTARY MUSCLE 81 



femur. Between the upper ends of the adductor longus and 

 the adductor magnus can be seen two small muscles, the adductor 

 brevis and the pectineus, both of which originate in the pubis and 

 are inserted in the proximal half of the femur. 



Muscles of the Thigh, Dorsal Side. — The vastus externus which 

 can be seen at the outer surface of the thigh in the ventral view, 

 is a part of the triceps femoris which can be better understood 

 from the dorsal view (Fig. 48). The triceps femoris forms the 

 front of the thigh and arises by three heads : (1) the vastus internus, 

 from the outer covering of the acetabulum at the junction of the 

 ischium and pubis; (2) the rectus femoris anticus, from the ventral 

 side of the middle of the ilium; and (3) the vastus externus, from 

 the crest of the ilium. The fibers of the rectus femoris anticus 

 join those of the other two components at the middle of the 

 thigh, forming a single muscle that is inserted by a single tendon 

 passing over the knee joint to the proximal end of the tibio- 

 fibula. Its action extends the cms and pulls the whole leg for- 

 ward. The semimembranosus is a large muscle occupying the 

 inner half of the dorsal surface of the thigh, arising from the 

 posterior margin of the ilium and, passing under an arch formed 

 by the tendon of origin of the gastrocnemius muscle, ends in a 

 tendon inserted on the dorsal surface of the tibiofibula. It is 

 divided obliquely into anterior and posterior halves by a tendi- 

 nous insertion. This muscle adducts the thigh and may extend 

 or flex the crus, depending upon whether the crus is in an extended 

 or flexed position when the muscle contracts. 



The pyriformis is a narrow muscle originating at the tip of 

 the urostyle and is inserted on the inner surface of the femur. 

 The iliopsoas extends from the ilium to the outer surface of the 

 femur. The gluteus arises from the posterior two-thirds of the 

 ilium and is inserted on the femur near the head. The biceps 

 or iliofibularis can be seen near the lower ends of the semimem- 

 branosus and the vastus externus. Its tendon of origin passes 

 from the ilium between the pyriformis and the iliopsoas, under 

 and behind the origin of the vastus externus. It has two points 

 of insertion: one on the inner surface of the femur and the other 

 on the dorsal surface of the femur and on the tibiofibula. 



Muscles of the Crus. — The gastrocnemius muscle forms the 

 calf of the leg or crus. One of its two heads arises from a tendi- 

 nous arch extending from the femur to the tibiofibula and the 



