Cfi. XLIY.j THE NINTH AND TENTH NERVES 645 



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, middle con- 

 strictor of pharynx, and crico-thyroid muscles, and probably to the 

 levator palati and other muscles of the palate, except the tensor, 

 which is supplied by the fifth nerve, and the other constrictors of 

 the pharynx, which are supplied from the nucleus ambiguus by cranial 

 rootlets of both ninth and tenth nerves. The nerve also contains 

 fibres concerned in common sensation, and the sense of taste, and 

 secretory fibres for the parotid gland. Whether the secretory fibres 

 in the chorda tympani which pass to the submaxillary and sublingual 

 glands originate from the seventh or ninth nerves is still uncertain. 



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 ganglia 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. 459). 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 are partly from the upper part of the combined nucleus, which 

 lower down gives origin to the spinal accessory nerve (fig. 459, X) 

 but mainly from the nucleus ambiguus, the position of which is 

 shown in fig. 459, coloured blue, and also in transverse section in fig. 

 463. 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. 459) ; the descending fibres, together with 

 similar ones derived from the glosso-pharyngeal nerve, pass down in 

 the descending root of vagus and glosso-pharyngeal, which is also 

 known as the funiculus solitarius. These fibres terminate by arbor- 

 ising around the cells of the grey matter that lies along its mesial 

 border (descending nucleus of vagus and glosso-pharyngeal). This 

 nucleus approaches the middle line as it descends, and finally 

 joins that of the opposite side over the central canal (commissural 

 nucleus). 



The eleventh nerve (spinal accessory) is wholly efferent : it arises 



