522 THE NERVOUS SYSTEM. 



Physiologic Properties of the Facial. The facial is, origi- 

 nally, a purely motor nerve, and whatever sensibility is possessed 

 by the parts to which it is distributed is not due to facial fibers, 

 but to anastomotic fibers from other nerves, principally the fifth. 

 The most pronounced function of the facial is its relation to ex- 

 pression. The so-called " expression " of the face is caused by 

 different degrees of contraction of the facial muscles, and the 

 different expressions, such as of fear, of anger, etc., are due to con- 

 traction of different muscles. The facial is therefore said to be 

 the " nerve of expression," and when it is divided and the muscles 

 paralyzed, the reason for this title is readily understood. 



Facial Paralysis. AVhen the facial nerve is divided or its 

 functions otherwise abolished, the following are the results : 



(1) Effect of Facial Paralysis on Facial Expression. A com- 

 plete loss of expression follows on the affected side ; the wrinkles 

 on that side are obliterated and the face is flattened. 



(2) Effect of Facial Paralysis on the Eye. The muscle which 

 closes the eye is the orbicularis palpebrarum ; this muscle is inner- 

 vated by the facial nerve, and in paralysis, therefore, the eye 

 remains permanently open, the power to close it being lost. Inas- 

 much as the act of winking is but a rapid partial closing of the eye, 

 this act is also abolished and the eyeball is liable to become dry. 

 The act of winking spreads the tears which keep the eye moist. 

 Unless provided against, this exposure of the eye may result in 

 injury (p. 519). 



(3) Effect of Facial Paralysis on the Mouth. The mouth is 

 drawn by the unparalyzed muscles to the unaffected side. It is 

 impossible to approximate the lips of the affected side to a tumbler 

 or cup ; consequently in drinking therefrom, unless the head is 

 thrown back, fluids will dribble from the corners of the mouth. 

 The buccinator muscle being paralyzed, food finds its way into 

 the space between the cheek and the gum, and mastication is 

 seriously impeded. The lips being paralyzed, the consonants b and 

 p cannot be pronounced distinctly. If the tongue is protruded, it 

 seems to be deviated toward the affected side ; but this is only ap- 

 parent, for if the mouth is placed in the normal position it will 

 be seen that the tongue is unaffected. 



(4) Effect of Facial Paralysis on Taste. Accompanying facial 

 paralysis may be impairment or abolition of the sense of taste. 

 Authorities are not agreed as to the explanation of this result, but 

 it is doubtless due to interference with the chorda tympani. Some 

 attribute it to the .influence which this nerve exercises over the 

 circulation in the tongue and on the secretion of saliva : others 

 regard the chorda tympani as the nerve of taste to the anterior 

 two-thirds of the tongue, and as taking part in forming the gusta- 

 tory nerve or lingual branch of the trigeminus. Indeed, there is 

 a difference of opinion among anatomists as to the true source of 

 the chorda tympani, at least so far as concerns those fibers which 



