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 lumbo- 

 sacral) 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 

 nerve. 



The femoral nerve is formed from the 

 fifth, sixth, and seventh lumbar, especially 

 from the loop 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 111). 



The internal pudendal nerve is formed from the loop connecting 

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

 from the second. 



no 



ms 



Fig. 78. Plan of the 

 lumbosacral plexus: L,S,0, 

 lumbar, sacral, and caudal 

 vertebrae; nl, ns, corres- 

 ponding spinal nerves; nf, 

 femoral nerve; no, obtur- 

 ator nerve; nis, sciatic 

 nerve; np, pudendal nerve. 



The Articulations of the Posterior Limb. 



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

 posterior limb make them much more favorable for examination 

 than the corresponding parts of the anterior limb. 



