404 NERVOUS SYSTEM. 
branches (perineal nerves) into the fat at the sides of the anus, 
and branches onto the lateral surface of the biceps muscle. One 
of the latter follows the communicating vein (Fig. 163, 2’) from 
V. saphena parva, and may be traced as far distad as the 
popliteal space. 
6. N. hemorrhoidalis inferior (or posterior) (Fig. 162, 7). 
—tThis arises by two roots, from the second and third sacral 
nerves, and passes with the inferior hemorrhoidal artery ventrad 
across the lateral surface of the rectum to the urethra. Here 
it divides into two parts: one passes craniad to the bladder, the 
other caudad onto the ventrolateral surface of the rectum. 
A small nerve passes from the sacral plexus, especially 
from the third sacral nerve, into M. levator ani (Fig. 162, 11). 
Another small nerve from the same region passes to M. coccy- 
geus, and a third to the proximal end of M. tenuissimus. 
E. NERVES OF THE TAIL. COCCYGEAL NERVES.— From 
the intervertebral foramina of the first seven or eight caudal 
vertebre spinal nerves of the usual type are given off. The 
dorsal rami innervate the dorsal muscles of the tail. The 
ventral rami are interconnected with each other and with the 
last sacral nerve by a longitudinal cord; they innervate the 
muscles and integument of the ventral side of the tail. 
3. The Sympathetic Nervous System. Systema nervo- 
rum sympathicum. 
The sympathetic system consists essentially of a chain of 
ganglia on each side of the ventral surface of the vertebral 
column, interconnected by longitudinal nerve-cords, and 
stretching from the base of the skull to the tail. The ganglia 
are connected to the spinal nerves by communicating branches, 
and numerous branches pass from them to the abdominal and 
thoracic viscera, and to the walls of the lymph- and blood- 
vessels, forming complicated plexuses. 
Cervical portion (Fig. 156, page 379).—The sympathetic 
system begins just caudad of the tympanic bulla as the superior 
cervical ganglion (G. cervicale superius) (Fig. 156, ¢). This 
is a large ganglion closely applied to the ganglion nodosum 
(2) of the vagus, and lying on its ventrocranial side. From 
