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 
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Fic: 78. Plan of -the 
lumbosacral plexus: L,S,C, 
lumbar, sacral, and caudal 
vertebrae; nl, ns, corres- 
ponding spinal nerves; nf, 
femoral nerve; no, obtur- 
ator nerve; nis, sciatic 
nerve; np, pudendal nerve. 
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- 
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 
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. 
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. 
