414 



PHYSIOLOGY 



passing inwards with the main root of the facial, divide into ascending and 

 descending branches and end in the upper part of the column of grey matter 

 which receives also the sensory fibres of the ninth and tenth cranial 

 nerves. 



The ninth and tenth cranial nerves arise by a series of bundles of nerve 

 fibres from the side of the medulla. Both the ninth and tenth are mixed 

 visceral sensory and motor nerves. The sensory nucleus is a column of 

 grey matter lying laterally to the hypoglossal nucleus just below the promin- 

 ence on the floor of the fourth 

 ventricle known as the ala 

 cinerea. The descending fibres 

 of these nerves form a well- 

 marked bundle of white fibres 

 known as the fasciculus soli- 

 tarius, or sometimes, from its 

 supposed connection with the 

 regulation of respiration, the 

 ' respiratory bundle of Gierke.' 

 It may be traced down as far as 

 the uppermost part of the cer- 

 vical cord, its fibres losing 

 themselves on their way down 

 among the cells of the enclosing 

 FIG. 206. Plan of the origin of the tenth and grey matter. The efferent fibres 



twelfth nerves. of the nmth and tenth nerveg 

 pyr, pyramid ; nXII, nucleus of hypoglossal ; -, . -, . , 

 XII, hypoglossal nerve ; dnX, XI, dorsal nucleus of are derived partly trom the 

 vagus and accessory ; n.amb, nucleus ambiguus ; dorsal nucleus of the vagUS and 

 js, fasciculus solitanus (descending root of vagus and , . 

 glossopharyngeal) ; fsn, its nucleus; X, crossing accessory nerves lying extern- 

 motor fibre of vagus ; g, cell in ganglion of vagus a H y to the nucleus of the twelfth 

 giving origin to a sensory fibre ; dV, descending root J 

 of fifth ; cr, corpus restiforme. nerve, and partly from the 



nucleus ambiguus, a mass of 

 grey'matter lying deeper in the medulla (Fig. 206). 



jp* The ninth or glossopharyngeal nerve supplies motor fibres to the muscles 

 of the pharynx and the base of the tongue, and secretory fibres to the parotid 

 gland. The sensory fibres convey impulses from the tongue, the mouth, and 

 pharynx, the fibres originating outside the central nervous system in the 

 ganglion- cells of the ganglion petrosum and the ganglion superius. It also 

 contains inhibitory fibres to the respiratory centre. 



The tenth nerve, vagus or pneumogastric, is joined by the accessory part 

 of the spinal accessory, so that the two nerves may be considered together. 

 It has both afferent and efferent functions : 

 Efferent functions : 



Motor to levator palati and three constrictors of pharynx. 



Motor to muscles of larynx. 



Inhibitory to heart. 



Motor to muscular walls of oesophagus, stomach, and small intestine. 



