538 



COMPARATIVE ANATOMY 



The somatic fibers act upon the hairs to stimulate their erection and 

 cause "goose flesh." They also serve the important function of regulating 

 temperature by influencing the tonus of the capillaries in the skin and 

 thus, by changing the rate of blood flow, altering the amount of secretion 

 of the sweat-glands. (Fig. 136) 



The course followed by sympathetic and parasympathetic fibers within 

 the central nervous system is almost unknown. Evidence is not lacking 

 that stimulation of the cerebral cortex may be followed by reactions of 

 the viscera. 



visceral motor 

 somatic motor 



visceral sensory 



somatic sensory 

 sympathetic. 



Pig. 444. — Diagram of the relations of the sympathetic system. The character of 

 the different fibers is shown by conventional lines, hv, blood-vessel; eg, chain ganglion; 

 d, dorsal ramus; dr, dorsal root; g, gland; gr, gray ramus; pc. Pacinian corpuscle; pg, 

 peripheral ganglion; pvg, prevertebral ganglion; sg, ganglion of dorsal root; st, sym- 

 pathetic trunk; v, ventral ramus; vi, visceral ramus; vr, ventral root; wr, white ramus. 

 (From Kingsley's "Comparative Anatomy of Vertebrates," based on Huber.) 



Three kinds of autonomic fibers connect with sympathetic ganglia. 

 Preganglionic fibers are visceral efferent fibers which come from ganglion 

 cells located in the lateral column of the spinal cord and have their ter- 

 minations in sympathetic ganglia. Post-ganglionic fibers are also 

 visceral efferent and have their cell bodies within sympathetic ganglia 

 and their telodendria upon smooth muscles of the intestine and of the 

 blood vessels. The preganghonic fibers are medulla ted and form the 

 white rami communicantes which connect spinal nerves with sympathetic 

 ganglia. The post-ganglionic fibers are rarely medullated. They pass 



