638 HUMAN ANATOMY. 



2. Semitendinosus (Fig. 608). 



Attachments. — The semitendinosus arises from the tuberosity of the ischium 

 in common with the long- head of the biceps. Its fibres extend downward to a long, 

 slender tendon, which passes behind the inner condyle of the femur and then curves 

 forward along with the tendon of the gracilis to be inserted^ below that tendon and 

 under cover of the expanded tendon of insertion of the sartorius, into the inner 

 surface of the tibia near the tuberosity. 



Nerve-Supply. — By the internal popliteal di\ision of the greater sciatic nerve 

 from the fifth lumbar and first and second sacral nerves. 



Action. — To extend the thigh and flex and rotate inward the leg. Acting from 

 below it will extend the trunk upon the hip-joints. 



Relations. — A large bursa (bursa anserina) intervenes between the tendons 

 of the gracilis and semitendinosus and the tibia. 



3. Semimembranosus (Fig. 609). 



Attachments. — The semimembranosus arises by a broad, flat tendon, which 

 extends from upper and outer facet upon the tuberosity of the ischium downward 

 along the outer border of the muscle to about the middle of the thigh. The muscle- 

 fibres pass downward and inward from this tendon to a tendon of insertion, which 

 occupies the medial border of the muscle and passes behind the inner condyle of the 

 femur and curves forwardto the inner surface of the internal condyle of the tibia, 

 into which it is inserted. An extension of the tendon of insertion usually passes 

 downward and outward to the portion of the deep fascia of the leg which covers the 

 popliteus muscle ; another band extends upward and outward towards the outer con- 

 dyle of the femur, blending with and materially strengthening the posterior part of 

 the capsular ligament of the knee-joint. 



Nerve-Supply. — By the internal popliteal division of the greater sciatic nerve 

 from the fourth and fifth lumbar and first sacral nerves. 



Action. — To flex the leg and assist somewhat in rotating it inward. Acting 

 from below it will extend the trunk upon the hip-joints. 



Relations. — The semimembranosus is situated in front of the long head of the 

 biceps and the semitendinosus and behind the adductor magnus. The greater 

 sciatic nerve lies along its lateral border (Fig. 606). The tendon of insertion is 

 separated from the inner head of the gastrocnemius by a bursa (bursa m. semimem- 

 branosi medialis), which often communicates with the synovial ca\ity of the knee- 

 joint ; the bursa m. semimembranosi lateralis intervenes between the tendon and the 

 inner condyle of the tibia. 



I. Sartorius (Fig. 610). 



Attachments. — The sartorius is a long band-like muscle which a7'ises from 

 the anterior superior spine of the ilium and the adjacent part of the notch below it. 

 It descends obliquely downward and inward across the front of the thigh, in the 

 groove between the rectus femoris and the vastus internus, on the on-^" hand, and the 

 adductor muscles, on the other, and then passes directly downward behind the 

 inner condyle of the femur. It finally bends forward to be inserted into the inner 

 surface of the tibia near the tuberosity, covering the insertions of the gracilis and 

 semitendinosus. 



Nerve-Supply. — By the anterior crural nerve from the second and third 

 lumbar nerves. 



Action.— To flex the thigh and leg and to rotate the thigh outward ; when 

 the leg is flexed, the muscle will assist in rotating the thigh inward. 



