AND PHYSIOLOGY. 351 



632. The optic nerve, as expanded in the retina, is the 

 nerve of sight. 



633. The auditory nerve receives the vibrations of the air. 

 which produce sound. 



634. The motores oculorum, pathetici, and abducentes are 

 the nerves which furnish motive power to the eye-ball. 



635. The facial nerve is distributed to the muscles of the 

 face, and is the one that aids in the expressions of the emo- 

 tions and will, as exhibited in the countenance. It is also the 

 channel of the reflex actions in respiration, as when a person 

 involuntarily gasps if cold water be dashed in the face. 



636. The lingual (hypoglossal) nerve is necessary for the 

 production of articulate speech, regulating and controlling as 

 it does the muscles of the tongue. 



637. The trifacial nerve administers the sense of touch to 

 the surface of the tongue, and aids somewhat in the sense of 

 taste. One branch of it is a muscular branch. Another is 

 sent to the mucous surface of the eye, and if it be cut off the 

 eye is destroyed by suppuration. 



638. The glosso-pharyngeal is the essential nerve of taste, 

 and is closely connected in function with the trifacial. It 

 seems also to be the nerve through which unpleasant sensa- 

 tions excited in the mouth are conveyed to the medulla ob- 

 longata so as to excite nausea and vomiting. 



639. The par vagum sends nervous power to the heart- 

 stomach, lungs, and larynx, as well as conveys to the braii* 

 any disagreeable sensations excited in these organs. Conse- 

 quently this is the essential nerve of digestion, respiration, 

 circulation, and opening or closure of the glottis under ordi- 

 nary circumstances. 



640. The spinal accessory seems to be the nerve by which 

 the regulation of the muscles essential to the production of 

 voice is effected. 



