SPINAL CORD AND COMMENCEMENT OF MEDULLA OBLONGATA. 191 



Please notice in Fig. 115 the position of the remnant of the 

 anterior horn and the great increase in volume of the olivary 

 bodies. TVhen the lateral horn is divided from the rest of the 

 gray matter there appears, at the point where, lower down, the 

 posterior horn was attached (a region, therefore, which, in the 

 spinal cord, was occupied by the nuclei of sensory nerves), a large 

 new nucleus with spindle-shaped cells much like those of the 

 posterior horns. This is the sensory nucleus of the vagus. It 

 lies on the floor of the rhomboidal fossa, internal to the ala 

 cinerea (Fig. 112), and extends forward to about the middle one 

 of the transverse white lines which you see crossing the fossa. 

 From this anterior end arises the glosso-pharyngeal nerve. The 

 nucleus of the glosso-pharyngeal is not sharply divided from 

 that of the vagus. We now see that there are two nuclei for 

 the vagus, a ventral one, which, from its situation (prolongation 

 of a portion of the anterior horn) and from its cells (multipolar 

 with axis-cylinders), we judge to be motor, and a dorsal one, 

 which, from its situation in the prolongation of the gray matter 

 at the base of the posterior horn and from its structure, we take 

 to be sensory. The first mentioned of these is also called the 

 nucleus ambiguus. The fibres arising from it all pass dorsad, 

 and unite and turn . at angle to join the straight sensory root, 

 which is much larger. (See Fig. 115.) Besides these two nuclei 

 the vagus receives fibres from at least two other regions. There 

 is a small fasciculus which can be traced from the cervical 

 medulla up to the point in the oblongata, where the last roots 

 of the glosso-pharyngeal arise. On its median side is a column 

 of gelatinous substance containing a few cells. The fibres from 

 these all pass to the fasciculus just mentioned. At the level of 

 the vagus-roots it begins to send off fibres to them, and this it 

 does to all the roots of the vagus and the glosso-pharyngeal. 

 This fasciculus is called the common ascending vago-pharyngeal 

 root.* 



It can be seen in Figs. 110 and 118, dorsad of the vagus- 



* Gierke's respiratory bundle. 



