PATHS OF THE CKANIAL NERVES 545 



The peripheral neurones of the centripetal or sensory portion 

 of the vagus, whose cell bodies lie in the jugular ganglion, enter 

 the medulla along with its motor fibres. They pass inward toward 

 the dorsal grey matter, at the border of which each fibre divides 

 into a short ascending and a long descending branch. The long 

 descending branches collectively form a small compact bundle of 

 medullated fibres, the tractus solitarius (fasciculus solitarius, 

 tractus spinalis nervi vagi). The fibres of this tract, after passing 

 caudad for a considerable distance, terminate about a group of 

 small nerve cells in the grey matter which surrounds the fasciculus, 

 the nucleus of the solitary tract. The cells of this nucleus acting 

 as neurones of the second order send their fibres, after the manner 

 of the internal arcuates, to join the mesial fillet of the opposite 

 side. 



The short ascending branches, together with many collaterals 

 from the descending processes, terminate about the small nerve 

 cells of the triangular or chief vagus nucleus in the floor of the 

 fourth ventricle. The cells of this nucleus, also acting as neurones 

 of the second order, send their neuraxes, in a manner similar to 

 those coming from the nucleus of the solitary tract, to the oppo- 

 site mesial fillet, and are continued through neurones of higher 

 orders to the cerebral cortex.* 



The ninth or glossopharyngeal nerve (Figs. 383 and 384). 

 The course of the neuraxes of this nerve is exactly similar to those 

 of the vagus. Its peripheral motor nerves begin as nerve cells of 

 the cephalic end of the nucleus ambiguus, those belonging to the 

 glossopharyngeal nerve not being in any way distinguishable from 

 those of the vagus except by their superior position. Their neu- 

 raxes pass dorsalward to meet the incoming sensory neurones, in 

 company with which they make their exit through the small 

 lateral columns of the medulla oblongata. 



The central motor neurones from the cerebral cortex arrive in 

 the nucleus ambiguus after traversing the corona radiata, internal 

 capsule, and pyramidal tracts ; they then decussate in the median 

 raphe, to terminate in arborizations about the nerve cells of the 

 opposite side in the same manner as do the central neurones of the 

 vagus path. 



The peripheral sensory (centripetal) neurones of the glosso- 

 pharyngeus begin as cell bodies in the petrosal ganglion, which, 

 like the other root ganglia of the cranial nerves, is homologous with 



* For the course of the mesial fillet, see page 531. 

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