CHAP. XIX.] THE FACIAL NERVE. 107 



eyelids depends on this nerve, as it alone supplies the orbicularis pal- 

 pebrarum ; and likewise that of frowning, from its influence upon the 

 corrugator supercilii. Anatomy indicates, therefore, that this nerve 

 is the motor nerve of the superficial muscles of the face and ear, 

 and of the deep-seated muscular fibres within the ear. 



This conclusion is abundantly confirmed by comparative anatomy. 

 For wherever the superficial muscles of the face are well developed, 

 and the play of the features is active, this nerve is large. In mon- 

 keys it is especially so. That extremely mobile instrument, the 

 elephant's trunk, is provided with a large branch of the facial as its 

 motor nerve. In birds, on the other hand, it is very small, being 

 limited to the stylo-hyoid branch. 



Section of the nerve, at its emergence from the stylo-mastoid fora- 

 men, has been followed by paralysis of the muscles of the face, and of 

 the orbicularis palpebrarum, in the hands of all experimenters. For- 

 merly when this nerve was supposed to preside over the sensibility 

 of the face, it .was thought to be the seat of tic douloureux, and was 

 upon several occasions cut. But this operation yielded no relief to 

 the sufferings of the patient, and only served to illustrate the func- 

 tion of the nerve, since it was always succeeded by paralysis of the 

 face on that side, total loss of control over the features, of the 

 power of frowning, and of closing the eyelids. 



The diseased states of the facial nerve illustrate its physiology 

 in the most interesting manner. It may be paralysed from the 

 influence of cold, benumbing its superficial fibres, or from the com- 

 pression of a tumor at the angle of the jaw, or from a carious state 

 of the petrous portion of the temporal bone. From whatever 

 cause the paralytic state arises, the effect is invariably the same; 

 the patient is unable to close his eyelids, and in some rare cases he 

 has not the power even of approximating them to each other in the 

 least degree. He cannot move the ala nasi or either lip on the 

 affected side, and if told to purse up the mouth, as in whistling, he 

 is unable to do it. When he laughs, the movement is all on one 

 side, and the angle of the mouth on the sound side is drawn up- 

 wards towards the ear, whilst that on the paralysed side hangs below 

 its ordinary level. With so much paralysis of the superficial mus- 

 cles, the deeper seated ones which direct the masticatory move- 

 ments of the lower jaw, and are supplied by the fifth nerve, remain 

 unaffected, and the sensibility of the face is unimpaired. 



When the paralytic affection of this nerve has been of long stand- 

 ing there is great wasting of the muscles on that side of the face, 

 and even the buccinator, which is supplied by the fifth nerve also, 



