232 



Anatomy of the Rabbit. 



The Lumbosacral Plexus. 



The structure of the lumbosacral plexus may be examined by 



breaking away the ventral portion of the pelvis, or by dividing the 



sacroiliac articulation in such a way that the two sides of the pelvis 



may be pressed apart, the ventral or pelvic face of the sacrum being 



thus exposed. The posterior portions of the 



psoas and iliacus muscles may be picked 



away with the forceps, and the abductor 



caudae anterior muscle (p. 270) may be 



detached from its origin on the ischial spine. 



The lumbosacral plexus (plexus lumbp- 



sacralis) is formed by the ventral roots of the 



four posterior lumbar and four sacral spinal 



nerves ' (Fig. 78). It is divisible into a 



lumbar plexus (plexus lumbalis) , from which 



arises the femoral nerve, and a sacral plexus 



(plexus sacralis) , from which arises the sciatic 



Fig. 78. Plan of the 

 lumbosacral plexus: L,S,C, 

 lumbscr, sacral, and caudal 

 vertebrae; nl, ns, corres- 

 ponding spinal nerves; nf, 

 femoral nerve; no, obtur- 

 ator , nerve ; nis, sciatic 

 nerve; np, pudendal nerve. 



The femoral nerve is formed from the 

 fifth, sixth, and seventh lumbar, especially 

 from the lo6p connecting the fifth and sixth 

 (ansa lumbalis 11). 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 dis- 

 tributed 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 III). 



The internal pudendal nerve is formed from the loop connecting 

 the second and third sacral nerves (ansa sacralis 11), but chiefly 

 from the second. 



TijE Articulations of the Posterior Limb. 



The more perfect development and larger size of the jdints of the 

 posterior limb make them much more favorable for examination 

 than the corresponding parts of the anterior limb. 



