FUNCTIONS OF THE CRANIAL NERVES. 265 



derived from its communications with the fifth and the pneumogastric 

 nerves. Its division, or injury, is accompanied by paralysis of all the 

 muscles of the face, excepting those supplied by the fifth nerve, i. e., 

 the masticatory muscles. In these cases, the mouth is distorted, being 

 drawn over to the opposite side by the unparalyzed muscles ; the act 

 of blowing out a candle is awkwardly performed, and is accompanied 

 by a puffing-out of the loose and paralyzed cheek ; whistling is im- 

 possible, and the attempt to smile causes a ludicrous expression ; 

 moreover, the eyelids cannot be closed, nor the skin of the forehead 

 thrown into wrinkles on the paralyzed side. The influence of this 

 nerve on the flow of the saliva has just been mentioned. In paralysis 

 of the orbicular muscle, which serves to close the eyelids in winking, 

 the movements of the eyeball itself are an imperfect substitute for the 

 action of the lids, in keeping the mucous membrane clean and moist, 

 and in directing the superfluous tears into the lachrymal passages ; 

 hence these escape over the cheek, and the mucous membrane of the 

 eyeball becomes inflamed. 



The glosso-pharyngeal nerve is chiefly an afferent nerve, being the 

 channel of sensation for the parts to which it is distributed. Some of 

 its fibres have the special power of conducting gustatory impressions, 

 viz., the branches which supply the root and sides of the tongue ; it is * 

 generally believed to be the nerve concerned in conveying disagreea- | 

 ble gustatory impressions to the medulla, and has been jocularly 

 named the disgustatory nerve. A few of its fibres are motor, viz., 

 those which supply certain palatal muscles. 



The vagus or pneumogastric nerve is a mixed afferent and efferent 

 nerve from its very origin, and does not, as some have supposed, de- 

 rive all its motor fibres from the spinal accessory nerve ; for irritation 

 of the pneumogastric within the cranium, before it communicates with 

 other nerves, causes contraction of the muscular fibres of the pharynx, 

 of the intrinsic muscles of the larynx, and of the fibres of the oesopha- 

 gus and stomach. It is a sensory, motor, and important excito-motor . 

 nerve. The sensations of pain, oppression, irritation of the air-pas- / 

 sages, want of air, hunger, thirst, and satiety, are dependent on this I 

 nerve. It has a regulating influence over the functions of deglutition, ' 

 digestion, circulation, and respiration. Division of one nerve in the 

 neck, causes difficulty of breathing, and interferes with the digestive 

 process. Division of both nerves is fatal, after a few hours or days, 

 in consequence of asphyxia. These results indicate, generally, the 

 office of this important nerve, which, however, is already joined, in the 

 neck, by branches from the glosso-pharyngeal, spinal accessory, and 

 hypoglossal nerves. After division of the right and left nerves, the 

 sensibility of the larynx and trachea disappears, and the reflex move- 

 ments, excited through them, such as coughing, cease. Owing to 

 paralysis of the laryngeal muscles, the vocal cords are relaxed, and 

 the voice is rendered hoarse and feeble, or entirely fails. The inspira- 

 tions are retarded, and an embarrassment of breathing is produced, 

 ending in suffocation ; this occurs more quickly in young animals, 

 owing to the want of development of the cartilaginous structures, and 

 the more yielding character of all the parts, so that the inter-aryte- 



