THE VISCERAL AFFERENT DIVISION. 



159 



superficial petrosal and main trunk of VII; pharyngeal and lin- 

 gual rami of IX; and pharyngeal, superior laryngeal, pulmonary, 

 oesophageal, gastric and sympathetic branches of the X nerve. 

 Possibly other branches also, such as the vidian nerve, carry fibers 

 of this component. 



Visceral sensory centers.— The brain centers in which the 

 visceral afi'erent fibers end in cyclostomes, ganoids, bony fishes, 

 amphibia and mammals have been found to be directly continuous 

 with the region of Clarke's column, namely, a column occupying 

 the mesial portion of the base of the dorsal horn. In all cases 

 these columns become greatly enlarged at about the junction of 

 the spinal cord and medulla oblongata, rise dorsally mesial to the 

 dorsal horns and join to form a median dorsal nucleus, the nucleus 



N.IX 

 N.Vll N.X 



N. branch. 1 



R- intest. 



R. palat.VII R. ling. IX R. pharyng. 



R. hyom. R. palat. IX R- posttr. 



R. prastr.Vll R- pratr. 



Fig. 80. — A simple diagram of the visceral nerves of the head in fishes. 



commissuralis, first described by Cajal in the mouse. The cells 

 of the nucleus commissuralis he imbedded among the fibers of a 

 commissure which has been known in fishes as the commissura 

 infima. Just cephalad of this nucleus and commissure the lateral 

 walls of the brain spread apart and are connected dorsally only 

 by the choroid plexus of the fourth ventricle. The visceral 

 columns now appear as more or less prominent ridges continuing 

 forward in the lateral walls of the fourth ventricle, which have 

 been described as including the vagal and facial lobes. 



As the visceral fibers in the X, IX and VII nerves enter these 



