THE POSTERIOR FEMORAL REGION. 519 



external intermuscular septum. The fibres of the long head form a fusiform 

 belly, which, passing obliquely doAvnward and a little outward, terminates in an 

 aponeurosis which covers the posterior surface of the muscle and receives the 

 fibres of the short head : this aponeurosis becomes gradually contracted into a 

 tendon, which is inserted into the outer side of the head of the fibula, and by 

 a small slip into the lateral surface of the external tuberosity of the tibia. At 

 its insertion the tendon divides into two portions, which embrace the long 

 external lateral ligament of the knee-joint, a strong prolongation being sent for- 

 ward to the outer tuberosity of the tibia, which gives off an expansion to the fascia 

 of the leg. The tendon of this muscle forms the outer hamstring. 



Relations. By its superficial surface, with the Gluteus maximus above, with 

 the fascia lata and integument in the rest of its extent; by its deep surface, 

 with the Semimembranosus, Adductor magnus, and Yastus externus, the great 

 sciatic nerve, and, near its insertion, with the external head of the Gastro- 

 cnemius, Plantaris, the superior external articular artery, and the external popliteal 

 nerve. 



The Semitendinosus, 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 

 facet on the tuberosity of the ischium by a tendon common to it and the long head 

 of the Biceps ; 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. 

 Ir forms 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. This tendon is surrounded by 

 the tendon of the Sartorius, and lies below that of the Gracilis, to which it is 

 united. A tendinous intersection is usually observed about the middle of the 

 muscle. 



Relations. By its superti<--ial surface, with the Gluteus maximus and fascia 

 lata : by its deep surface, with the Semimembranosus, Adductor magnus, inner 

 head of the Gastrocnemius, and internal lateral ligament of the knee-joint. 



The Semimembranosus, so called from the membranous expansion on its 

 anterior and posterior surfaces, is situated at the back part and inner side of the 

 thigh. It arises by a thick tendon from the upper and outer facet on the back 

 part of the tuberosity of the ischium, above and to the outer side of the Biceps 

 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 aponeurosis which covers the 

 upper part of its anterior surface : from this aponeurosis muscular 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 two fibrous expansions ; one of these, of considerable size, 

 passes upward and outward to be inserted into the back part of the outer con- 

 dyle of the femur, forming part of the posterior ligament of the knee-joint. The 

 second is continued downward to the fascia which covers the Popliteus muscle. 

 The tendon also sends a few fibres to join the internal lateral ligament of the 

 joint. 



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

 inner hamstring. 



Relations. By its superficial surface, with the Semitendinosus, Biceps, and 

 fascia lata : by its deep surface, with the popliteal vessels, Adductor magnus, and 

 inner head of the Gastrocnemius, from which it is separated by a synovial bursa ; 

 by its inner border, with the Gracilis; by its outer border, with the great sciatic 

 nerve and its internal popliteal branch. 



Nerves. The muscles of this region are supplied by the great sciatic nerve. 



Actions. The hamstring muscles flex the leg upon the thigh. When the 



