344 



THE NERVOUS SYSTEM 



(2) The axons may run through a connecting nerve trunk into another ganglion. 

 He is not able to say whether these axons only run through the second ganglion 

 or whether they make connections with its cells. In the chick embryo he at one 

 time described collaterals coming from those longitudinal fibers of the ganglia, 

 which take origin in neighboring ganglia. Now, however, he is inclined to doubt 

 this observation, and thinks it likely that these collaterals all come from fibers 

 that have entered the sympathetic trunk through white rami at other levels. 



Fig. 254. 



Fig. 255. 



Figs. 254 and 255. Preganglionic fibers and pericellular plexuses of the frog. Fig. 254, Pre- 

 ganglionic fibers, the branches of which form pericellular plexuses; Fig. 255, a unipolar sympathetic 

 ganglion cell in connection with which a preganglionic fiber is terminating. Methylene-blue. 

 (Huber.) 



(3) In some cases the axons, arising from cells in the ganglia of the sympathetic 

 trunk, run toward the neighboring arteries in the visceral nerves. 



There is no anatomic evidence worth mentioning in favor of the existence of association 

 neurons, uniting one sympathetic ganglion with another or one group of cells with another 

 within such a ganglion. But there is strong physiologic evidence against the existence of 

 such association neurons (Langley, 1900 and 1904) ; and Johnson (1918) has shown that none 

 are present in the sympathetic trunk of the frog. 



Termination of the Preganglionic Fibers. The spaces among the cells of a 

 sympathetic ganglion are occupied by a rich intercellular plexus of dendritic 



