404 NER.YOUS 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, ') from 

 V. saphena parva, and may be traced as far distad as the 

 popliteal space. 



6. N. hemorrhoidalis inferior (or posterior) (Fig. 162, /). 

 This 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 

 vertebra; 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. Sy sterna 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, e). This 

 is a large ganglion closely applied to the ganglion nodosum 

 (d) of the vagus, and lying on its ventrocranial side. From 



