DISSECTING MANUAL. 



lies under its insertion, and another between it and the Sarto- 

 rius. [373] 



Semimembranosus. Origin; upper and outer facet on 

 ischial tuberosity, by a tendon which soon develops a fleshy 

 belly. Insertion; horizontal groove on back of inner tuber- 

 osity of tibia (mainly) ; posterior border of internal lateral liga- 

 ment, by a fascial band which runs downward and inward; 

 oblique line of tibia, by a fascial band which runs downward 

 and outward and covers the Popliteus; back of external con- 

 dyle, by a fascial band which runs upward and outward, form- 

 ing the posterior ligament of the knee. [374] 



The popliteal space is lozenge-shaped, lies in the hollow be- 

 hind the knee, and is widest opposite the joint. It is bounded 

 externally by the Biceps above the joint, and the Plantaris and 

 outer head of Gastrocnemius below; and internally by the 

 Semimembranosus and Semitendinosus above, and the inner 

 head of the Gastrocnemius below. Its floor is formed by the 

 femur, knee-joint capsule, tibia, and fascia over the Popliteus. 



NERVES. 



Posterior Spinal Nerves. Lower thoracic; the external cu- 

 taneous branches of the two lowest supply the buttock. First, 

 second, and third lumbar; the external cutaneous branches sup- 

 ply the buttock to below and behind the great trochanter. 

 First, second, and third sacral; loops between them, often joined 

 by branches of the fifth lumbar and fourth sacral, form a 

 plexus (posterior sacral) on the back of the sacrum; the ex- 

 ternal cutaneous branches of the plexus pierce the sacro-sciatic 

 ligament and Gluteus maximus to supply the buttock. Fourth 

 and fifth sacral and coccygeal; these unite (posterior sacro- 

 coccygeal nerve) , pierce the sacro-sciatic ligament, and supply 

 the skin over the coccyx. [613] 



Anterior Spinal Nerves. Eleventh thoracic; the lateral cu- 

 taneous branch extends over the iliac crest. Twelfth thoracic; 

 the lateral cutaneous (iliac) branch descends over the front of 



[278] 



