NUCLEI <>!'' Till' CRANIAL .YAATA'N so.-, 



tioiis that they may lie described together. Moth cinitaiii efferent fibres, though 

 both an- in water part sensory. 'I'hcy an- very similar as in the origin (if 

 Imtli their efferent and afferent components. The afferent fibres of the vagus ; 

 in its tranu'lion juunlarc and its gantrlion nodnsuni (irandion of the trunk): the af- 

 ferent fibres of tin- giosso-pharyngeus arise in its ganglion superius and its ganglion 

 petrosnin. In both nerves these fibres enter the lateral aspect of the medulla and 

 bifurcate Into ascending and descending branches, similar to those of the dorsal root- 

 fibres in the spinal cord. Some of t hoe branches terminate in practically the same 

 level of the medulla about cell-bodies situated on the same and the oppo.-ite sides. 

 Such end chiefly in the nuclei of the hypoglossal and spinal accessory, and about 

 the cells giving origin to the efferent components of the vagus and glosso-pharyngeus 

 themselves short reflex fibres. However, most of the afferent fibres terminate in 

 the nucleus of termination of the vagus and glosso-pharyngeus: 0) the nucleus of 

 the ala cinerea, the middle portion of which is indicated in the floor of the fourth 

 \entrir-le by the ala cinerea: ('_') in the closed portion of the medulla, the lower end 

 of the nucleus of the ala cinerea comes to lie in the dorso-lateral proximity of the 

 central canal, and t his port ion is known as the commixxiirnl inicli UK <>j tin- nln cnu red 

 digs. ."'.):> and .">!7) from the fact that fibres may be seen which pass directly from 

 it across the mid-line: (3) most of the descending branches of the bifurcated fibres 

 collect to form the solitary tract, a compact bundle situated dorsally just lateral 

 to the nucleus of the ala cinerea and quite conspicuous in sections of the medulla. 

 The fibres of this bundle terminate in the nurlfiis of tin xotittiri/ tract, which is but a 

 ventro-lateral and downward continuation of the nucleus of the ala cinerea enclosing 

 the bundles forming the tract. It is probable that the fibres of the solitary tract 

 are chiefly from the vagus (pneumogafltric), though Bruce lias found evidence that the 

 glosso-pharyngeal contributes to it appreciably. It decreases rapidly in descending 

 the medulla, owing to the rapid termination of its fibres about the cells of its nucleus, 

 but it is believed to extend as far downwards ae the level of the fourth cervical segment 

 of the spinal cord. This being in the level or origin of the phrenic nerve, the funiculus 

 maybe in part a link in the respiratory apparatus which aids in the co-ordinated 

 respiratory movements. The axones given off by the cells of the terminal nuclei of 

 the vagus and glosso-pharyngeus course on both sides of the mid-line, the greater por- 

 tion perhaps decussating to be distributed to the structures of the opposite side. 

 Some join the lemniscus of the opposite side and pass into the cerebrum; others are 

 distributed to the motor neurones of the medulla and cervical cord of the same and 

 opposite sides (reflex axones), and no doubt others form central connections with the 

 cells of the retieular formation of the medulla, though their precise relations have 

 not been determined. 



The nuclei of origin of the motor fibres of the vagus and glosso-pharyngeus are 

 the dorsal efferent nucleus and the nucleus ambiguus. The cells of the dorsal 

 nucleus lie somewhat clustered in the ventro-mesial side of the nucleus of the ala 

 cinerea and lateral to the nucleus of the hypoglossus. Their axones pass outwards 

 among the entering or afferent vago-glossopharyngeal fibres. The nucleus am- 

 liiijiius or ventral efferent nucleus lies in the lateral half of the retieular formation, 

 about mid-way between the olive and the line traversed by the rootlets of the two 

 nerves. It.s upper end is larger. Its cells are considerably dispersed by the fibres 

 of the retieular formation. The axones arising from its cells course at first dorsal- 

 wards and then turn abruptly outwards to join the rootlets of the vagus or glosso- 

 pharyngeus, as the case may be. The vagus is thought to receive more efferent fibres 

 from the two motor nuclei than does the glosso-pharyngeus. and Cunningham notes 

 that it may be questioned whether the latter contains any motor fibres at all, there 

 being paths by which the fibres of its motor branch (to the stylo-pharyngeus mus- 

 cle) might enter it other than direct from the motor nuclei. 



The acoustic nerve is a double nerve, both divisions of which are purely sensory. 

 It enters the brain at the lateral aspect of the junction of the medulla oblongata and 

 pons. It is best described as t wo nerves: 



(1) The vestibular nerve arises as the central processes of the bipolar cells of 

 the natilnilnr <i<ui</li<i . and passes into t he brain-stem on t he inner side of the rest i- 

 form body to find its nucleus of termination (nucleus vestibularis) in the floor of the 

 fourth ventricle. This nucleus occupies a triangular area of considerable extent 

 (area actlstica. figs. .7.11 and ~>!M). and is usually subdivided into a Intern/ iiue/niN 

 (Deiters')i a medial nucleus (Schwalbe's), a tii/m-inr niti-li-us (Bechterew's), and an 



