546 THE NERVOUS SYSTEM. 



depended directly on the infra-orbital nerve ; for he found 

 that, after he had divided that nerve on both sides in an 

 ass, it no longer seized the food with its lips, but merely 

 pressed them against the ground, and used the tongue for 

 the prehension of the food. Mr. Mayo corrected this error. 

 He found, indeed, that after the infra-orbital nerve had 

 been divided, the animal did not seize its food with the lip, 

 and could not use it well during mastication, but that it 

 could open the lips. He, therefore, justly attributed the 

 phenomena in Sir C. Bell's experiments to the loss of 

 sensation in the lips ; the animal not being able to feel the 

 food, and, therefore, although it had the power to seize it, 

 not knowing how or where to use that power. 



Lastly, the fifth nerve has an intimate connection with 

 muscular movements through the many reflex acts of 

 muscles of which it is the necessary excitant. Hence, when 

 it is divided, and can no longer convey impressions to the 

 nervous centres to be thence reflected, the irritation of the 

 conjunctiva produces no closure of the eye, the mechanical 

 irritation of the nose excites no sneezing, that of the tongue 

 no flowing of saliva ; and although tears and saliva may 

 flow naturally, their afflux is not increased by the me- 

 chanical or chemical or other stimuli, to the indirect or 

 reflected influence of which it is liable in the perfect state 

 of this nerve. 



The fifth nerve, though its ciliary branches and the 

 branch which forms the long root of the ciliary or ophthal- 

 mic ganglion, exercises also some influence on the move- 

 ments of the iris. When the trunk of the ophthalmic 

 portion is divided, the pupil becomes, according to Valentin, 

 contracted in men and rabbits, and dilated in cats and 

 dogs ; but in all cases, becomes immovable, even under all 

 the varieties of the stimulus of light. How the fifth nerve 

 thus affects the iris is unexplained ; the same effects are 

 produced by destruction of the superior cervical ganglion 

 of the sympathetic, so that, possibly, they are due to the 



