444 CRANIAL NERVES. 



tion of the oesophagus is alone paralysed, and deglutition 

 can still be accomplished with tolerable ease. 



The pharyngeal branch is the principal motor nerve of the 

 pharynx and palate, and assists as well in giving motor power 

 to the tracheal part of the gullet. The superior laryngeal, too, 

 besides its action on the gullet, is the sensory nerve of the 

 mucous membrane of the larynx, and it is owing to its keen 

 sensibility, that the contact with the latter of a solid body, or 

 irritant gas or liquid, gives rise to violent and uncontrollable 

 fits of coughing. It is the motor nerve to a single laryn- 

 geal muscle, the crico-thyroid. The inferior laryngeal nerve, 

 besides conveying to the brain the impression for the reflex 

 action of the tracheal part of the oesophagus, and conferring 

 on the latter its somewhat dull sensibility, has for its prin- 

 cipal function the conveying of motor power to the muscles 

 of the larynx. It is distributed to all the muscles that enlarge 

 the glottal orifice ; and, accordingly, when cut, the freedom 

 of breathing is interfered with, and during rapid inspiration 

 a sound of a more or less shrill character is heard. The 

 animal in this case becomes a roarer, and the disease known 

 as " roaring" frequently depends on a lesion of this nerve. 

 If the nerves are injured on both sides, breathing becomes 

 correspondingly more difficult. This nerve has the further 

 function of modifying the* voice, by varying the tension of 

 the vocal cords. 



The branches of the pneumogastric furnished to the lungs 

 are the channels through which is conveyed that peculiar 

 impression which leads to the continuance of the respi- 

 ratory process. It is not, however, the sole agent for con- 

 veying this impression, since the non-aerated blood in all 

 parts of the body transmit a similar influence through the 

 various nerves, and respiration continues for a considerable 

 time after the division of both pneumogastrics. When a 



