THE NERVOUS SYSTEM 1495 



but it also contains a few efferent or motor fibres, which arise within 

 the medulla oblongata. 



AfiFerent or Sensory Fibres. — These fibres arise from the central 

 poles of the bipolar cells of the jugular and petrous ganglia, which 

 are situated on the glosso-phar\-ngeal nerve as it passes through 

 the jugular foramen. These ganglia resemble the Gasserian ganglion 

 of the fifth nerve and the spinal ganglia. Ha\nng entered the 

 medulla oblongata, the afferent fibres end in t«o terminal sensory 

 nuclei — namely, the dorsal vago-glosso-pharyngeal nucleus, and the 

 nucleus of the fasciculus solitarius. 



The dorsal vago-glosso-pharyngeal nucleus consists of two parts — 

 upper and lower. The upper part is situated in the grey matter of 

 the floor of the lower or bulbar part of the fourth ventricle, imder- 

 neath the superficial area known as the trig07ium vagi {ala cinerea), 

 and immediatelv exiertuU to the h}-poglcssal nucleus. The loTJcer 

 part is situated in the lower or closed part of the bulb, and lies in 

 the grey matter which forms the lateral wall of the central canal of 

 the bulb, being here situated behijid the h^'pcglossal nucleus. 



The highest part of the dorsal vago-glosso-phan-Tigeal nucleus 

 represents the portion associated with the glosso-phar^Tigeal nerve, 

 and the remaining and greater part belongs to the vagus ner^-e. 



The nucleus of the fasciculus solitarius is a column of grey matter 

 and nerve-cells which accompanies the fasciculus solitarius, to be 

 presently described, throughout the whole length of the medulla 

 oblongata. 



A few of the afferent fibres of the glosso-phar\Tigeal ners^e enter 

 the highest part of the dorsal vago-glosso-phar\Tigeal nucleus, and 

 terminate in arborizations around its cells. The most of the afferent 

 fibres, however, descend along with a few of the afferent fibres of 

 the vagus nerve, the two sets of descending fibres constituting a 

 strand, called the fasciculus solitarius {iractus solitarius B.) or 

 respiratory bundle. This strand descends throughout the whole 

 length of the medulla oblongata. It hes external to the dorsal 

 vago-glosso-phar\Tigeal nucleus, inclining towards the ventral aspect 

 of the upper part of that nucleus, and towards the dorsal aspect of 

 its lower part. It is accompanied throughout by the nucleus of 

 the fasciculus solitarius, and the glosso-pharynigeal afferent fibres 

 of the fasciculus solitarius terminate, at different levels, in arboriza- 

 tions around its cells. The fasciculus soHtarius is formed chieflv, 

 if not entirely, by glosso-phar\Tigeal fibres. The fasciculus soli- 

 tarius and its nucleus are comparable to the spinal or descending 

 fibres (root) and lower sensory nucleus of the fifth ner\'e. 



Efferent or Motor Fibres.— These fibres arise within the medulla 

 oblongata as the axons of some of the cells of the ventral vago- 

 glosso-pharyngeal nucleus or nucleus ambiguus. This nucleus is 

 situated iu the formatio reticularis grisea of the medulla oblongata, 

 and is in line ^\^th the facial motor nucleus which is placed in the 

 dorsal part of the lower portion of the pons Varolii. Both of these 

 nuclei correspond to the motor cells of the ventral grev comu of 



