DISSECTION OP THE DOG 



113 



region. The constitution of the nerves arismg from the lumbar and sacral 

 plexus may be summarised in this place. 



N. ilio-hypogastricus is formed by the first lumbar. 



N. ilio-inguinalis consists mainly of fibres derived from the second lumbar 

 nerve, but has, in addition, a reinforcement from the first lumbar. 



N. genito-femoralis generally contains fibres from the third and fourth 

 lumbar nerves, but occasionally those from the fourth are absent. 



N. cutaneus femoris lateralis is mainly formed by the fourth lumbar nerve, 

 but it also receives a branch from the third. 



N. femoralis is constituted by the union of two main roots from the fifth 

 and sixth lumbar nerves, with an occasional thin root from the fourth nerve 

 in addition. 



n. pitdendu3 



n. hcemorrhoidalis 

 caudalis 



n. Uio-inguinaliA 



n. ischiadicus 



n, ohtura 

 torius 

 n. glutcEus 

 craniaJis 



n. femoralis 

 Fig. 43. — Plexus of lumbar and sacral nerves. 



n. cutaneus 

 femoris 

 lateralis 



N. obturatorius results from the conjunction of three roots : namely, from 

 the fourth, fifth, and sixth lumbar nerves. 



N. ischiadicus is formed by the fusion of large roots from the sixth and 

 seventh lumbar nerves, and a smaUer root from the first sacral nerve. 



N. glutceus cranialis receives its fibres from the same spinal nerves as 

 does the sciatic nerve. 



N. glutceus caudalis contams fibres contributed by the first and second 



sacral nerves. 



N. pudendus has roots from the first, second, and third sacral nerves. 



N. cutaneus femoris posterior is formed by the second and third sacral nerves. 



N. hcemorrhoidalis caudalis is composed of fibres derived from the first 

 and second sacral nerves. 



With the exception of the obturator and caudal hsemorrhoidal nerves, 

 all the above have been examined. 



N OBTTjRATOEius.— The obturator nerve is of considerable size, and is 

 formed by roots which jom medial to the iUo-psoas muscle. The nerve crosses 

 the medial surface of the ilium and enters the obturator foramen by msmuatmg 



