164 COMPARATIVE MORPHOLOGY OF VERTEBRATES. 
peripheral ganglia, situated at various points along the viscera, some at 
some distance from the sympathetic centres. 
In the sympathetic system four kinds of nervous elements are to be 
distinguished. The original trunk that grows out (the ramus visceralis) 
consists of motor and sensory fibres. The latter arise from ganglion 
cells in the ganglia of the dorsal roots. The motor fibres have their 
cell bodies in the cord at about the level of the lateral cornu, and pass 
visceral motor 
a : H somatic motor 
<q "Peg f De _ wtsceral sensory 
sbeveecineeadeeee somatic sensory” 
{) 
db, edo gna 
PF NL KAngw Spe 
Fic. 166.—Diagram of the relations of the sympathetic system, based on Huber. ‘The 
character of the different fibres is shown by conventional lines. bv, blood-vessel; cg, chain 
ganglion; d, dorsal ramus; dr, dorsal root; g, gland; gr, gray ramus; pg, peripheral gangiion; 
pug, prevertebral ganglion; st, sympathetic trunk; v, ventral ramus; vi, visceral ramus; vr, 
ventral root; wr, white ramus. 
out, in the lower vertebrates by the dorsal, in the mammals by the 
ventral root. In the sympathetic system itself there are sensory and 
motor (excitatory) cells, derived from the ganglion cells carried down 
by the growing nerves. These develop their dendrites and axons, 
and some of these run up the rami communicantes to the dorsal and 
ventral rami, and follow along them to the peripheral glands and 
blood-vessels of the body. Others grow into the various viscera. These 
purely sympathetic fibers are not medullated and hence are gray in 
