178 TOPOGRAPHICAL ANATOMY OF THE 



N. femoralia, when it possesses its most widespread origin, receives 

 fibres from the third, fourth, fifth and sixth lumbar nerves ; but the 

 third often fails to contribute. The root from the fifth lumbar nerve is 

 the largest. 



N. obturatorius has three roots, derived from the fourth, fifth and 

 sixth lumbar nerves. The largest contribution comes from the fifth, 

 and the smallest from the fourth nerve. 



N. ischiadicui^, the largest nerve from the plexus, arises by large 

 roots from the sixth lumbar and the first and second sacral nerves, and 

 occasionally by a much smaller bundle of fibres from the third sacral 

 nerve. 



N. glutceus cranialis is composed of fibres from the sixth lumbar 

 and first sacral nerves. 



N. glutceus caudalis. N. cutaneus femoris posterior. — As a rule 

 each of these nerves is formed by the union of two roots : one composed 

 of fibres from the first and second, and the other from the second and 

 third sacral nerves. 



iV. ^mdendus is formed by the third and fourth sacral nerves. 



A\ hcemorrhoidalis caudalis results from the union of a large root 

 from the fourth sacral nerve and a smaller root from the third. A 

 slender root may also be derived from the fifth sacral nerve. 



Of the above nerves the undermentioned remain to be dissected. 



N.i OBTURATORIUS. — After its formation by the roots above 

 mentioned, the obturator nerve passes in a ventral and caudal direction^ 

 in relation to the external iliac vein as far as the pelvic brim. It then 

 follows the cranial face of the obturator vein, accompanies this vessel 

 underneath the pubic head of the internal obturator muscle, and gains 

 the thigh by traversing the obturator foramen. Its ultimate distribu- 

 tion to muscles on the medial aspect of the thigh is disclosed during 

 the dissection of the pelvic limb. 



N. GLUTiEUS CRANIALIS. N. GLUTEUS CAUDALIS. N. CUTANEUS 



FEMORIS POSTERIOR. N. iscHiADicus. — The gluteal, posterior 

 cutaneous and sciatic nerves quickly make their exit by the greater 

 sciatic foramen, and are encountered in the dissection of the gluteal 

 region of the pelvic limb. 



Nn. COCCYGEI. — Leaving the vertebral canal between the first six 

 vertebrae of the tail are five coccygeal nerves. Each nerve divides into 

 dorsal and ventral branches, after the manner of spinal nerves in 

 general. All the dorsal and all the ventral branches join to form 

 dorsal and ventral nerves respectively on each side of the tail. The 



