724 A MANUAL OF PHYSIOLOGY 



acustica, a series of prominent strands that run transversely across the 

 floor of the fourth ventricle, consist of fibres arising in the accessory 

 nucleus and the acoustic tubercle, and form a portion of this central 

 path. Two prominent symptoms may be associated with disease of 

 the auditory nerve (a) disturbance or loss of hearing ; (I)) loss or 

 impairment of equilibration. 



The ninth, or glosso-pharyngeal, the tenth, or vagus, and the 

 eleventh, or spinal accessory nerves, may be considered together. 

 They are connected with an elongated nucleus in the medulla 

 oblongata, the upper portion of which is especially related to the 

 glosso-pharyngeal, the middle to the vagus, and the lower to that 

 division of the spinal accessory which arises from the medulla, and 

 which may, therefore, be called the bulbar accessory. Since the 

 fibres of the nerves related to this nucleus pass into it from the 

 nerve-roots to form synapses with its cells, it must be looked upon 

 not as a nucleus of origin for these fibres, but as a nucleus of 

 reception. An additional nucleus of reception for some of the 

 afferent fibres is supplied by scattered cells in the lateral grey matter of 

 the cord as far down as the fourth cervical nerve, and in the formatio 

 reticularis of the medulla. The fibres passing down to arborize 

 around these cells form a bundle, called the fasciculus solitarius, or, 

 since they belong mainly to the ninth nerve, the ascending root of the 

 glosso-pharyngeal. The cells of origin of these afferent fibres are uni- 

 polar ganglion cells of somewhat the same type as those of the spinal 

 ganglia. They are situated in various ganglia connected with the 

 vagus (ganglion jugulare and ganglion nodosum) and with the 

 glosso-pharyngeal (ganglion petrosum and ganglion superius). Their 

 central processes become the afferent axons of the nerve-roots, their 

 peripheral processes pursue their course as the axons of sensory fibres 

 to the structures to which the nerves are distributed. A motor 

 nucleus of origin is the nucleus ambiguus, which lies in the recti- 

 cular formation of the bulb. The axons of its cells proceed mainly 

 to the vagus, although some of them may enter the other two nerves. 

 The spinal portion of the spinal accessory is a purely motor nerve. 

 Its cells of origin lie in the lateral horn of the cord from about the 

 level of the first to the sixth or seventh cervical nerves. Some 

 authors consider that the bulbar accessory is also entirely motor, 

 but this is probably erroneous. 



The glosso-pharyngeal has both sensory and motor fibres sensory 

 for the posterior third of the tongue and the mucous membrane of the 

 back of the mouth, motor for the middle constrictor of the pharynx 

 and the stylo-pharyngeus. It also contains the nerves of taste for the 

 posterior third of the tongue, but these reach it from the fifth nerve. 



The vagus contains both sensory and motor fibres, the latter 

 partly derived from the accessory, whose internal branch joins it 

 not far from its origin. The distribution of the nerve is more 

 extensive than that of any other in the body. The oesophagus 

 receives both motor and sensory branches from the cesophageal 

 plexus. The pharyngeal branch of the vagus is the chief motor 

 nerve of the pharynx and soft palate (including the tensor palati). 

 The superior laryngeal branch is the nerve of common sensa- 



