CHAP. VII.] 



THE NERVOUS SYSTEM. 



79 



stomach, and other viscera in the trunk ; they also enter the 



cranium, send branches to the organs of special sense, and, 



in particular, influence 



the pupil of the eye. 



Their most important 



distribution, however, 



is in connection with 



the blood-vessels. 



They form plexuses 



around the vessels, 



/ -^/flfflMBMirffiy y jjp 1 ^'/ / f\ 



especially the arteries, / 



and send fibres to ter- 

 minate in the involun- 

 tary muscular tissue 

 of which the walls of 

 these tubes are largely 

 composed. The nerves 

 thus distributed are 

 called " vaso-motor " 

 nerves. 



In the sympathetic 

 ganglia the relation of 

 the neurones is such 

 that each nerve-fibre, 

 arriving at the gan- 

 glion from the spinal 

 cord, is brought into 

 contact with several 

 other neurones which 

 lie wholly in the sym- 

 pathetic system. Thus 

 an efferent impulse, 

 passing along an axone 

 from the cord, may 

 pass to the dendrones 

 of several sympathetic 



cells, and then by their FIG. 67. GENERAL VIEW OF THE SYMPATHETIC 



, , ,, SYSTEM. 1, 2, 3, cervical ganglia ; 4, 1st thoracic 



axones tO the Smooth gan g] ion . 5> lst lumbar ganglion ; 6, 7, sacral gan- 



muscles of the viscera, S lion ; 9 9 > cardiac nerves; 13, branch of pneumo- 



gastric nerve ending in semi-lunar ganglion ; 14, 



or to similar endings, epigastric plexus. 



