542 THE CRANIAL NERVES. 



filaments from the facial. After paralysis of this nerve, therefore, 

 complete closure of the lids becomes impossible, although the move- 

 ments of the eyeball are unaffected, and the pupil is capable of dilata- 

 tion and contraction as before. 



At the same time the motion of winking is suspended upon the 

 affected side. This movement is an involuntary reflex action, excited 

 by the contact of air with the surface of the cornea, and the accumula- 

 tion of the tears along the edge of the lower eyelid. At short intervals 

 this produces an instantaneous contraction of the orbicularis, by which 

 the edges of the eyelids are brought together, and again immediately 

 separated ; thus spreading the moisture of the lachrymal secretion uni- 

 formly over the cornea and protecting its surface from dryness or irri- 

 tation. After section of the facial nerve, this movement ceases, and 

 on thrusting a solid body suddenly toward the face of the animal it can 

 be seen that the eye on the sound side instinctively closes, while the 

 other remains open. Even touching the conjunctiva or the cornea on 

 the operated side fails to cause contraction of the eyelids, although the 

 animal shrinks and the eyeball turns in the orbit; showing that the 

 motor power of the orbicularis alone has been affected while sensibility 

 remains. 



Two precisely opposite effects, accordingly, are produced upon the 

 movements of the eye, by section of the fifth nerve, or its ophthalmic 

 branch, and by that of the facial. After division of the fifth nerve, 

 touching the cornea fails to produce closure of the eyelids because the 

 sensibility of its surface has been destroyed, though the power of motion 

 remains. When the facial has been divided, it is the muscular action 

 which is paralyzed, the sensibility of the parts remaining entire. 



Effect on the Nostrils. In some animals, as in man, the nostrils are 

 more or less rigid and nearly inactive in the ordinary condition. They 

 expand, however, with considerable vigor when the movements of 

 respiration are increased in frequency, or when the air is forcibly in- 

 spired to assist in the sense of smell. In many species, furthermore, 

 as in most graminivorous quadrupeds, and especially in the horse, they 

 alternately expand and collapse in a regular and uniform manner, with 

 each inspiration and expiration ; executing in this way a series of 

 respiratory movements synchronous with those of the chest and abdo- 

 men. Even in man the expansion of the nostrils, at the time of in- 

 spiration, becomes very marked whenever the breathing is hurried or 

 laborious, owing to increased muscular exertion or to any accidental 

 obstruction of the air-passages. 



All these movements are suspended by section of the facial nerve. 

 The muscles by which they are performed being paralyzed, the nostril 

 on the affected side becomes flaccid, and, instead of opening for the 

 admission of air into the nares, it collapses and forms more or less of 

 an obstruction to its entrance. As the partial dyspnoea thus induced 

 tends to accelerate the breathing, the paralyzed nostril is still further 

 compressed by the air in the movement of inspiration; while at the 



