470 THE NERVOUS SYSTEM. 



side. The visible effects vary in the different facial regions, according 

 to the function of the paralyzed muscles. 



Effect on the Eye. Owing to paralysis of the orbicularis oculi, the 

 eye on the affected side cannot be closed ; according to Bernard it re- 

 mains open even while the animal is asleep. This depends on the fact 

 that the muscles serving to open and close the eyelids are animated by 

 different nerves ; the levator palpebrse superioris, which lifts the upper 

 eyelid, being supplied by the oculomotorius, while the orbicularis oculi 

 receives its filaments from the facial. In paralysis of the facial, there- 

 fore, complete closure of the lids is impossible, although the movements 

 of the eyeball and pupil are unaffected. 



At the same time the movement of winking is suspended on the 

 affected side. This is a reflex action, caused by the contact of air with 

 the surface of the cornea, and the accumulation of tears along the edge 

 of the lower eyelid. At short intervals this excites a momentary con- 

 traction of the orbicularis, by which the eyelids are brought together, 

 and again immediately separated ; thus spreading the lachrymal secre- 

 tion uniformly over the cornea and protecting it from desiccation. 

 After section of the facial nerve, this movement ceases ; and if a solid 

 body be suddenly thrust toward the face of the animal, the eye on the 

 sound side instinctively closes, while the other remains open. Even 

 touching the cornea on the operated side fails to cause contraction of 

 the eyelids, although the animal shrinks and the eyeball turns in its 

 orbit ; showing that sensibility remains, although the motor power of 

 the orbicularis is lost. 



Precisely opposite effects, accordingly, are produced by section of the 

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

 ing the cornea fails to produce closure of the eyelids because the sensi- 

 bility of the surface has been destroyed, though the power of motion 

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

 lyzed, and sensibility remains entire. 



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

 nostrils are nearly motionless in the ordinary state of respiration. They 

 expand, however, with considerable vigor when the breathing is in- 

 creased in frequency, or when the air is forcibly inspired to assist the 

 sense of smell ; and in many quadrupeds they exhibit regular move- 

 ments of expansion and collapse, synchronous with those of the chest 

 and abdomen. In man, this action becomes very marked whenever 

 the breathing is hurried or laborious, owing to muscular exertion or 

 obstruction of the air-passages. 



These movements are suspended by section of the facial nerve. The 

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

 for the admission of air, it collapses and forms an obstruction to its 

 entrance. As the dyspnoea thus induced tends to accelerate respiration, 

 the paralyzed nostril is still further compressed in inspiration ; and at 

 expiration it is forcibly extruded by the outgoing current. The natural 

 movements of the nostril are therefore reversed by paralysis of the 



