40 



drawn aside. Near the posterior border of the M. gluteus proftindus the 

 small nerve to the gemelli, etc., (in cases where only one nerve is present), 

 gives off a small branch which passes through the lesser sciatic foramen 

 into the pelvic cavity where it divides into two branches one of which 

 extends anteriorly along the surface of the iliac portion of the M. obturator 

 internus to which it is distributed; the other branch supplies the other 

 head of the obturator internus (PI. V, 50). The main nerve itself crosses 

 the deep or internal face of thegemelliandthetendon of the obtiirator internus, 

 supplies branches to the gemelli and may be seen again at the posterior 

 border of this muscle where it enters the adjoining quadratus femoris (PI. 

 IV, 27). Demonstrate this by carefully separating the adjoining borders 

 of the gemelli and quadratus femoris in order to expose the nerve. The 

 gemelli and the tendon of the obturator internus may now be transected 

 in order to expose completely the nerve and its branches as above men- 

 tioned. 



N. ischiadicus (PI. V, 54; PI. IV, 26) arises from the 5th and 6th lumbar 

 and the ist and 2d sacral nerves; occasionally it receives a branch from the 

 3d sacral nerve. It passes through the great sacro-sciatic foramen and 

 between the sacro-sciatic ligament and the M. gluteus medius, crosses a 

 portion of the gluteus profundus, the gemelli and the tendon of the obturator 

 internus and the quadratus femoris. Near the level of the gemelli the 

 N. ischiadicus divides into two terminal branches — peronaeus communis 

 and N. tibialis (PI. IV, 29, 34). (It should be -kept in mind that the N. 

 ischiadicus and its branches are named differently by different authors. 

 The names here given are the names used in the more recent text books of 

 anatomy and are the terms recommended by the various National Ana- 

 tomical Societies.) In the femoral region the Nn. peronaeus communis 

 and tibialis are svirrounded by the biceps femoris, the adductor magnus 

 and the semimembranosus. Near the level of the gemelli there is given off, 

 either from the N. ischiadicus or from the N. tibialis, a large fasciculus 

 which extends somewhat posteriorly and supplies the biceps femoris, semi- 

 tendinosus and semimembranosus (PL IV, 28). Demonstrate, by dissect- 

 ing between the biceps femoris and the semitendinosus and between the 

 semitendinosus and the semimembranosus. Transect the semitendinosus 

 at the level of the 3d trochanter and trace the nerve branches to their 

 respective m.uscles. 



N. peronaeus communis (PI. IV, 29). The distal portion of the biceps 

 femoris must now be turned aside, noting the blood-vessels, which must 

 be cut, that enter the muscle and also the small nerve — peronaeal cutaneous 

 (PI. IV, 30, 30') — a branch of the N. peronaeus communis. This small 



