Chap. XIX] THE NERVOUS SYSTEM 397 



cells of origin, like those of the abducens nerve, are situated in the 

 medulla. 



(8) The auditory nerve is the special nerve of the sense of hear- 

 ing. It arises from cells which compose the organ of Corti in the 

 internal ear, to which its fibres are exclusively distributed. 



(9) The glossopharyngeal nerve is distributed, as its name 

 indicates, to the tongue and pharynx, being the nerve of sensa- 

 tion to the mucous membrane of the pharynx, of motion to the 

 pharyngeal muscles, and the special nerve of taste to part of the 

 tongue. 



(10) The pneumogastric nerve has a more extensive distribu- 

 tion than any of the other cranial nerves, passing through the neck 

 and thorax to the upper part of the abdomen. It contains both 

 motor and sensory fibres. It supplies the organs of voice and 

 respiration with motor and sensory filaments ; and the pharynx, 

 oesophagus, stomach, and heart with motor fibres (cardiac inhibi- 

 tory). 



(11) The spinal-accessory nerve consists of two parts : one, the 

 spinal portion, and the other, the accessory portion to the tenth 

 nerve. It is a motor nerve supplying certain muscles of the neck. 

 It differs from the other cranial nerves in arising from the spinal 

 cord, but it leaves the skull by the same aperture as the pneumo- 

 gastric and glossopharyngeal. 



(12) The hypoglossal nerve is the motor nerve of the tongue. 

 Reflex acts. — The student doubtless can understand from 



the preceding portions of this chapter the general arrange- 

 ment of the nervous tissues, and how simple impulses arising 

 in brain cells pass along nerve-fibres, and, terminating in the 

 end organs, produce, for example, a muscular contraction (mo- 

 tor impulse), or how an outside stimulus applied to the skin 

 will set up vibrations in suitable end organs to be transmitted 

 along sensory nerve-fibres to end in sensory brain cells and pro- 

 duce the appreciation by the mind of the fact that the stimu- 

 lus has been applied. All of these are simple, straightforward 

 functions of the neurones. There is a host of other more com- 

 plex acts in which, for example, two or more neurones take part, 

 which carry out a train of functions, each depending on the other, 

 and may carry out their destiny so smoothly and accurately, so 

 that the perception of the mind or consciousness of the act 



