678 STRUCTURE OF THE BULB, PONS, AND MID-BRAIN [CH. XLYI. 



The ninth nerve (glosso-pharyngeal) gives filaments through its 

 tympanic branch (Jacobsen's nerve) to parts of the middle ear; 

 also, to the carotid plexus, and through the great superficial petrosal 

 nerve to the spheno-palatine (Meckel's) ganglion. After communi- 

 cating, either within or without the cranium, with the vagus, it leaves 

 the cranium, divides into the two principal divisions indicated by 

 its name, and supplies the mucous membrane of the posterior and 

 lateral walls of the upper part of the pharynx, the Eustachian tube, 

 the arches of the palate, the tonsils and their mucous membrane, 

 and the tongue as far forwards as the foramen caecum in the middle 

 line, and to near the tip at the sides and inferior part. 



It contains motor fibres to the stylo-pharyngeus, the constrictors 

 of the pharynx, and probably to the levator palati and other muscles 

 of the palate, except the tensor, which is supplied by the fifth nerve. 

 The nerve also contains fibres concerned in common sensation, and 

 the sense of taste, and secretory fibres for the parotid gland. 



The cells from which the motor fibres originate are situated in a 

 special nucleus, which is a continuation upwards of the nucleus 

 ambiguus (the chief motor nucleus of the tenth or vagus nerve). The 

 sensory fibres arise in the jugular and petrosal gangSa from cells of 

 the spinal ganglion type. When the central axons reach the bulb 

 they bifurcate as usual; the descending branches pass down the 

 funiculus solitarius and terminate in synapses around the cells 

 scattered among its fibres. The ascending branches pass almost 

 horizontally to arborise around the cells of the principal nucleus 

 (IX. in fig. 408). The arrangement, in fact, is very like that of the 

 tenth nerve now to be described. 



The tenth nerve (vagus or pneumo-gastric) has so many and 

 important functions that I shall not attempt to describe them here ; 

 it would mean rewriting a great deal of what we have already learnt 

 in connection with heart, respiration, digestion, etc. It is sufficient 

 to say that it contains both efferent and afferent fibres. The efferent 

 fibres arise partly from the upper part of the combined nucleus, which 

 lower down gives origin to the spinal accessory nerve (fig. 408, X.) but 

 mainly from the nucleus ambiguus, the position of which is shown in 

 fig. 408, coloured blue, and also in transverse section in figs. 412 and 

 418. The afferent fibres originate from the cells of the ganglion of 

 the trunk and of the root ; they enter the bulb and bifurcate ; the 

 ascending branches are short and arborise around the cells of the 

 principal nucleus (X. in fig. 408) ; the descending fibres, together with 

 similar ones derived from the glosso-pharyngeal nerve, and pars 

 intermedia, pass down in the descending root of vagus and glosso- 

 pharyngeal, which is also known as the funiculus solitarius. These 

 fibres terminate by arborising around the cells of the grey matter 

 that lies along its mesial border (descending nucleus of vagus and 



