362 THE ANATOMY OF THE HOHSE. 



nerve, and is then expended in the skin of the anus and root of 

 the tail. 



As in other regions of the spine, each of the inferior primary branches . 

 just considered communicates with the contiguous ganglion of the 

 sympathetic cord, by one or more branches detached at the inter- 

 vertebral foramen ; and the sacral nerves send each a filament to the 

 pelvic plexus. 



The Sympathetic Gangliatbd Cord in the sacral region. This is the 

 direct backward continuation of the lumbar cord. It is placed on the 

 inferior surface of the sacrum, internal to the inferior sacral foramina, 

 the lateral sacral artery intervening between it and the inferior primary 

 branches of the sacral nerves at their points of emergence. It possesses 

 a ganglion opposite each of the first three sacral foramina; and, as before 

 said, it communicates by filaments passing between these ganglia and 

 the corresponding spinal nerves. The emergent branches of these 

 ganglia are very slender, and pass to the cellular tissue beneath the 

 sacrum, or to the contiguous blood-vessels. The cord terminates at the 

 last ganglion, either abruptly, or by a filament passing on to the middle 

 coccygeal artery. 



The Internal Iliac Artery (Plate 48). This is one of the terminal 

 branches of the posterior aorta. Beginning at the intervertebral disc 

 between the 5th and 6th lumbar vertebree, it passes downwards and 

 backwards across the articulation between the last lumbar transverse 

 process and the sacrum, and then across the sacro-iliac articulation ; and 

 at the upper part of the ilio-pectineal line, a little above the eminence of 

 the same name, it divides into the iliaco-muscular and obturator arteries. 

 The vessel is covered by the peritoneum, and in the first inch or two of 

 its course it is separated from the external iliac artery by the common 

 iliac vein. The collateral branches of the internal iliac, taken in the 

 order of their points of detachment, are as follows : — 



1. The second last of the series of lumbar arteries arises from the in- 

 ternal iliac at its root. It behaves like the lumbar branches of the aorta. 

 Its upper division, much the larger of the two, passes upwards through 

 the intervertebral foramen between the 5th and 6th lumbar vertebrae. 



2. The Internal Pudic Artery. This is a considerable vessel, which 

 has its origin at the last lumbar vertebra. Entering the pelvis, it 

 descends at the ischiatic edge of the ilium, and then passes backwards 

 in the texture of the sacro-sciatic ligament, or on its inner face. 



3. The Lateral Sacral Artery leaves the parent trunk at the sacro- 

 lumbar articulation; and passes backwards on the lower face of the. 

 sacrum, beneath or at the inner side of the inferior sacral foramina. 

 A little behind the middle of the sacrum it divides into the ischiatic and 

 lateral coccygeal arteries. The former, much the larger of the two, passes 

 out through the edge of the sacro-sciatic ligament to reach the hip 



