THE CRANIAL NERVES AND THEIR NUCLEI 



181 



visceral afferent fibers. The majority of the taste fibers run through the seventh 

 (via the chorda tympani and lingual) and ninth nerves (Gushing, 1903), but a 

 few reach the epiglottis by way of the tenth (Wilson, 1905 Fig. 129). All 

 cf these general and special visceral afferent fibers, whether contained in the 

 seventh, ninth, or tenth nerves, enter the tractus solilarius, within which they 

 descend for varying distances (Fig. 120, yellow). They terminate in a column 

 of nerve-cells, which in part surround the tract and in part are scattered among 

 its fibers. This is known as the nucleus of the tractus solitarius (Figs. 121, 130). 

 It is a long slender nucleus, which extends throughout the entire length of the 

 medulla oblongata and is best developed at the level of origin of the vagus nerve, 



Fig. 129. Diagram of the trigeminal, facial, and glossopharyngeal nerves showing the course 

 of the taste fibers in solid black lines. The broken and dotted lines indicate the course which ac- 

 cording to certain investigators some of the taste fibers are supposed to take: G. G., Gasserian 

 ganglion; G. g., geniculate ganglion; G. sp., sphenopalatine ganglion; g.s.p., great superficial petro- 

 sal nerve; N. Jac., the tympanic nerve of Jacobson; N. vid., vidian nerve; s.s.p., small superficial 

 petrosal nerve. (Gushing.) 



where it lies ventrolateral to the dorsal motor nucleus of that nerve and some 

 little distance below the floor of the fourth ventricle (Fig. 103). The fibers 

 from the seventh and ninth nerves terminate in the rostral portion of the 

 nucleus, which is therefore the part especially concerned with the sense of taste, 

 while those from the vagus end in the caudal part. Some of these vagus fibers 

 after undergoing a partial decussation terminate in a cell mass, the commissural 

 nucleus, which lies dorsal to the central canal in the closed part of the medulla 

 and unites the nucleus of the tractus solitarius on one side with the correspond- 

 ing nucleus on the other side (Fig. 121). 



The secondary afferent paths from the nucleus of the tractus solitarius are 

 not well denned. Since gustatory impulses arouse sensations of taste and the 



