Integrative Systems 179 



ganglions, is entered by the visceral trunk (ramus communicans) of 

 the corresponding spinal nerve (Figs. 152, 158). The ganglions in the 

 cervical region receive no incoming fibere from cervical spinal nerves, 

 but are entered by systems of fibers which arrive in the autonomic cord 

 via the rami communicantes of several thoracic spinal nerves and then 

 extend forward, or else send branches forward, to all the cervical gan- 

 glions (Fig. 159). The ganglions in the head are connected with certain 

 cranial nerves (Figs. 157, 159). The ciliary ganglion lies on a branch 

 of the oculomotor (HI). The sphenopalatine, sublingual, and 

 submaxillary are connected to branches of the facial (VII), and the 

 otic ganglion is on the glossopharyngeal (IX). 



In the midtrunk region is a group of large ganglions which are apart 

 from the main autonomic cords, lying in the dorsal mesentery. Al- 

 though of duplex origin, each is a single median ganglion. There are 

 usually three (Figs. 157, 159), a celiac, an anterior mesenteric, and 

 a posterior mesenteric, each lying in close relation to the artery of 

 the same name. These three "collateral ganglions," as they are 

 called, are connected with the spinal cord by paired splanchnic 

 nerves (Fig. 157, 18, 19), each formed by union of parts of the rami 

 communicantes of several spinal nerves of the thoracolumbar re- 

 gion. A splanchnic nerve is essentially a much-elongated ramus com- 

 municans. Therefore the relation of the collateral ganglions to the 

 spinal cord is like that of the lateral ganglions, except as to position. 



From one or another of these ganglions — lateral, collateral, and 

 cephalic — nerves pass to the coelomic viscera and to structures, where- 

 ever situated, which possess smooth muscles or secretory cells. It is to 

 be remembered, too, that in addition to the extrinsic ganglions are the 

 intrinsic ganglions and plexuses of the viscera themselves. These in- 

 trinsic ganglions are sometimes called "terminal." The cephalic gan- 

 glions, in that each is situated very close to the organ with which it is 

 concerned, resemble terminal ganglions rather than the lateral and 

 collateral ganglions. 



Functional Components of Autonomic Nerves 



The foregoing description is concerned only with the gross anatomy 

 of the autonomic system. Appreciation of its mode of operation re- 

 quires some knowledge of the nature and relations of the constituent 

 neurons of the system. 



A typical or complete ramus communicans of a spinal nerve con- 

 tains afferent fibers whose cell-bodies are in the dorsal root ganglion 

 of the spinal nerve, and efferent fibers whose cell-bodies are in the 

 gray matter of the spinal cord (Figs. 152, 158). These visceral efferent 

 fibers constitute the great majority of the fibers that pass into the 



