430 THE NERVOUS SYSTEM. 



physiology of the nerves. He supposed that the motion of 

 the upper lip, in grasping food, 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 cor- 

 rected this error. He found, indeed, that after the infra-or- 

 bital 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 sen- 

 sation in the lips ; the animal not being able to feel the food, 

 and, therefore, although it had the power to seize it, not know- 

 ing 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 mechanical 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, through its ciliary branches and the branch 

 which forms the long root of the ciliary or ophthalmic gan- 

 glion, exercises also some influence on the movement 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 stimu- 

 lus of light. How the fifth nerve thus affects the iris is unex- 

 plained ; the same effects are produced by destruction of the 

 superior cervical ganglion of the sympathetic, so that, possibly, 

 they are due to the injury of those filaments of the sympathetic 

 which, after joining the trunk of the fifth, at and beyond the 

 Gasserian ganglion, proceed with the branches of its oph- 

 thalmic division to the iris ; or, as Dr. R. Hall ingeniously 

 suggests, the influence of the fifth nerve on the movements of 

 the iris may be ascribed to the affection of vision in conse- 

 quence of the disturbed circulation or nutrition in the retina, 

 when the normal influence of the fifth nerve and ciliary gan- 

 glion is disturbed. In such disturbance, increased circulation 

 making the retina more irritable might induce extreme con- 

 traction of the iris ; or, under moderate stimulus of light, pro- 



