43R CRANIAL NERVES. 



sensory; but they nevertheless exercise considerable influ- 

 ence over the facial muscles by presiding over their mus- 

 cular sense. They are further the natural excitants of many 

 reflex actions in the facial muscles. That they are not 

 motor is proved by Longet's experiment of stimulating them 

 with galvanism, which produced excessive pain, but no 

 convulsions. In the same way the lower maxillary division 

 confers sensibility on the muscles, integuments, &c., of the 

 lower jaw with this addition, that it is the motor nerve of 

 the muscles of mastication. When cut on one side, masti- 

 cation is performed with difficulty, and entirely on the 

 opposite side, and the animal falls off rapidly in condition. 

 This division supplies, moreover, through its lingual branch, 

 the special sense of taste to the anterior half of the tongue, 

 so that this sense depends on two nerves, the glosso-pharyn- 

 geal and trifacial. On the integrity of this nerve depends 

 indirectly the activity of the secretion in the lachrymal and 

 salivary glands ; an irritant touching the eye, or a sapid sub- 

 stance the tongue, producing an impression on the nervous 

 centres, which through reflex action leads them to secrete. 

 It is very interesting to notice the influence which this 

 nerve exerts over the nutrition of several structures the 

 seats of special senses. The division of the nerve, or of its 

 ophthalmic branch, causes immediate contraction of the 

 pupil, and in less than twenty-four hours acute inflamma- 

 tion of the conjunctiva and opacity of the cornea; followed 

 by a purulent discharge; the iris becomes involved and 

 loses all power of movement, and sight is lost, though the 

 optic nerve and retina are unaffected. These results come 

 on much more slowly if the section is made between the 

 Gasserian ganglion and the brain, which seems to indicate 

 that they depend in greater part, though not entirely, on 

 the fibres of the sympathetic received at this point 



