BACK OF THE THIGH 323 



as to form a groove, in which the semitendinosus lies. The 

 tendon of insertion is attached chiefly to the floor of the 

 groove on the back of the medial condyle of the tibia, under 

 cover of the tibial collateral ligament of the knee joint. Three 

 additional attachments, however, must be noted. These are 

 effected by aponeurotic extensions from the tendon of in- 

 sertion (i) to the back of the capsule of the knee joint, 

 forming a considerable part of the oblique popliteal ligament ; 

 (2) to the surface of the popliteus muscle, which is covered 

 by the expansion ; and (3) to the tibial collateral ligament of 

 the knee joint. The semimembranosus is supplied by the 

 sciatic nerve. Its actions are the same as those of the 

 semitendinosus (see p. 322). 



Nervus Ischiadicus (O.T. Great Sciatic Nerve). The 

 sciatic nerve commences at the lower border of the greater 

 sciatic foramen, and usually terminates about the middle of the 

 thigh, but occasionally at a higher level, by dividing into the 

 tibial nerve and common peroneal nerve. Its relations in 

 the gluteal region have already been studied. In the thigh 

 it lies on the posterior surface of the adductor magnus muscle, 

 and is covered by the long head of the biceps femoris. It 

 gives branches to both heads of the biceps, to the semi- 

 tendinosus, to the semimembranosus, and to the adductor 

 magnus ; the branches to the two last-named muscles arise 

 by a common trunk. In a few cases it gives off a long 

 articular twig, which enters the popliteal fossa and takes the 

 place of the lateral superior articular nerve, which, as a rule, 

 is a branch of the common peroneal nerve. 



Dissection. To bring the adductor magnus more fully into 

 view, and to facilitate the cleaning of its posterior surface, and 

 at the same time to follow the terminal parts of the perforating 

 arteries, the hamstring muscles should be detached from their 

 origins and thrown distally. First detach the common tendon 

 of the biceps femoris and semitendinosus from the ischial tuber- 

 osity. When that has been done the exact attachment of the 

 semimembranosus is displayed, and after that muscle has been 

 again examined, under the present more advantageous circum- 

 stances, it also must be detached from its origin and turned 

 distally. The posterior surface of the adductor magnus will 

 then be fully exposed, and its attachment to the femur and its 

 relations to the perforating arteries can be studied. 



Arterise Perforantes. Four perforating arteries will be 

 found in the posterior part of the thigh between the adductor 

 magnus muscle and the femur, close to the linea aspera. 



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