THE POSTERIOR LIMB 



289 



Iv 



nf 



Ivi 



m ^^" 



SI 



ns ^ 



npci 



np 



Fig. 106. Ventral view 

 of right lumbosacral 

 plexus, cl, first caudal 

 nerve; 1 IV- VII, fourth 

 to seventh lumbar 

 nerves (ventral rami) ; 

 nf, femoral nerve; ng, 

 gluteal nerves; no, 

 obturator nerve ; np, 

 pudendal nerve ; npc, 

 posterior cutaneous 

 nevye ; ns, sciatic nerve ; 

 sI-IV, first to fourth 

 sacral nerves. 



abductor caudae anterior muscle (p. 343) 

 may be detached from its origin on the 

 ischial spine. 



The lumbosacral plexus (plexus lumbo- 

 sacralis) is formed by the ventral roots of the 

 four posterior lumbar and four sacral spinal 

 nerves (Fig. 106). It is divisible into a lum- 

 bar plexus (plexus lumbalis), from which 

 arises the femoral nerve, and a sacral plexus 

 (plexus sacralis), from which arises the sciatic 

 nerve. It is subject to certain variation. 



The femoral nerve is formed usually 

 from the fifth, sixth, and seventh lumbar, 

 especially from the loop connecting the fifth 

 and sixth (ansa lumbalis ii). The obturator 

 nerve (n. obturatorius), which accompanies 

 the obturator artery, is formed from the fifth, 

 sixth, and seventh lumbars but chiefly from 

 the sixth, and is distributed to the obturatores, 

 adductores, and gracilis muscles. 



The sciatic nerve, together with the 

 superior and inferior gluteal nerves, arises 

 chiefly from the loop connecting the last 

 lumbar and first sacral nerves (ansa lumbalis 



in). 



The internal pudendal nerve is formed 

 from the loop connecting the second and third 

 sacral nerves (ansa sacralis ii) , but chiefly from 

 the second, and the posterior cutaneous nerve 

 may also connect with the same roots. 



The Articulations of the Posterior Limb 

 The more perfect development and larger 

 size of the joints of the posterior limb make 

 them much more favourable for examination 

 than the corresponding parts of the anterior 

 limb. 



The muscular attachments should be re- 



