526 THE MUSCLES AND FASCIAE 



thin expansion is given off to the fascia of the leg. The tendon of this muscle 

 forms the outer Hamstring. 



Relations. By its superficial surface, with the Gluteus maximus and the small sciatic nerve, 

 the fascia lata, and integument. By its deep surface, with the Semimembranosus, Adductor 

 magnus, and Vastus externus, the great sciatic nerve, and, near its insertion, with the external 

 head of the Gastrocnemius, the Plantaris, the superior external articular artery, and the external 

 popliteal nerve. A bursa (bursa m. bicipitis femoris inferior) is found between the long tendon 

 of origin of this muscle and the Semitendirrosus and Semimembranosus. Sometimes there is a 

 bursa (bursa bicipitogastrocnemialis) between the tendon of the insertion of the Biceps and the 

 origin of the Gastrocnemius, and there is a bursa (bursa m. bicipitis femoris inferior) between 

 the tendon of the Biceps and the external lateral ligament. 



The Semitendinosus (m. semitendinosus) (Figs. 387 and 391), remarkable 

 for the great length of its tendon, is situated at the posterior and inner aspect 

 of the thigh. It arises from the lower and inner impression on the tuberositv 

 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 three inches after their origin. The Semitendi- 

 nosus is a fusiform muscle, which, passing downward and inward, terminates a 

 little below the middle of the thigh in a long round tendon which lies along the 

 inner side of the popliteal space, then curves around the inner tuberosity of the 

 tibia, and is inserted into the upper part of the inner surface of the shaft of that 

 bone nearly as far forward as its anterior border. At its insertion it gives off 

 from its lower border a prolongation to the deep fascia of the leg. This tendon 

 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 muscles. The bursa anserina lies between the tendon of the Semitendinosus 

 and the tibia. 



The Semimembranosus (m. semimembranosis) (Figs. 387 and 391), so called 

 from its membranous tendon of origin, is situated at the back part and inner 

 side of the thigh. It arises by a thick tendon from the upper and outer impression 

 on the back part of the tuberosity of the ischium, above and to the outer side of 

 the Biceps femoris and Semitendinosus, and is inserted into the groove on the 

 inner and back part of the inner tuberosity of the tibia, beneath the internal 

 lateral ligament. The tendon of the muscle at its origin expands into an apon- 

 eurosis which covers the upper part of its anterior surface; from this aponeurosis 

 muscle fibres arise, and converge to another aponeurosis, which covers the lower 

 part of its posterior surface and contracts into the tendon of insertion. The 

 tendon of the muscle at its insertion gives off certain fibrous expansions; one of 

 these, of considerable size, passes upward and outward, to be inserted -into the 

 back part of the outer condyle of the femur, forming part of the posterior ligament 

 of the knee-joint; a second is continued downward to the fascia which covers 

 the Popliteus muscle. The tendon also sends a few fibres to join the internal 

 4ateral ligament of the joint. 



The tendons of the two preceding muscles, with that of the Gracilis, form the 

 inner Hamstrings. 



Nerves. The muscles of this region are supplied by the fourth and fifth lumbar and the 

 first, second, and third sacral nerves through the great sciatic nerve. 



Actions. The Hamstring muscles flex the leg upon the thigh. When the knee is semiflexed, 

 the Biceps, in consequence of its oblique direction downward and outward, rotates the leg 

 slightly outward; and the Semitendinosus, and to a slight extent the Semimembranosus, rotate 

 the leg inward, assisting the Popliteus. Taking their fixed point from below, these muscles, 

 especially the Semimembranosus, serve to support the pelvis upon the head of the femur and 

 to draw the trunk directly backward, as in raising it from the stooping position or in feats of 

 strength, when the body is thrown backward in the form of an arch. When the leg is extended 

 on the thigh, they limit the amount of flexion of the trunk on the lower limbs. 



