Many of those cases of paralysed facial nerve, which occur in the human subject as the effect of disease involving their structure, approximate closely to the results obtained by an artificial division of the nerve in animals ; but in consequence of the much more ex pressive character of the human countenance in the normal state, the deviations produced are even of a more striking appearance. One half of the face forms a perfect blank, its muscles hanging passively from the subjacent structures ; while the movements of the opposite side are distorted by the absence of their proper antagonist motions, and are ex aggerated in appearance by the contrast.
In the experiments above mentioned, Sir Charles Bell found that immediately on di viding the nerve the muscular aperture of the nostril, which had previously been subject to an alternate dilatation and contraction during the periods of inspiration and expiration respectively, suddenly lost this movement. He has termed the portio dura the respiratory nerve of the face ; since it presides over these and other motions of the facial muscles, which are developed independently of the will, and in answer to the necessities of res piration.
The section of the facial nerve indirectly affects the sense of smell. This fact was also first pointed out by Sir Charles Bell, and has since been confirmed by many other observers. Under these circumstances, the power of discerning strong odors as tobacco and ammonia, appears to be much' diminished on the affected side, although scarcely abso lutely lost. This loss of smell has been ascribed to the absence of two causes greatly conducive to the exercise of this faculty in health. The muscular contraction of the nostril which accompanied the effort of snuffing effects a considerable narrowing of the aperture ; and in the deep inspiration which accompanies the act, the rapidity of the entering current of air is thus greatly augmented, and in this greater velocity is implied an increased contact of the odorous vapour with the sensitive surface. Besides this, the direction of the current of air seems .to be somewhat altered ; the muscles, tending much more to constrict the posterior than the anterior parts of the orifice, appear to direct the current more upwards or anteriorly than in the ordinary inspiration. The me chanical nature of the action has been illus trated by Diday*, who has shown that dila tation of the nostrils by a glass tube, through which the air may be respired, equally pre• vents the perfect exercise of the olfactory sense ; and Longet confirms his exeeriments.
The effect of division of the porno dura on the eye is still more important. There is complete inability to close the eyelids of the affected side. This permanently open state is due to the action of the levator palpebr, unopposed by the paralysed orbicularis pal pebrarum ; and the eye itself, no longer pre served from the contact of foreign bodies, or swept over by the conjunctiva which lines the eyelids, is often irritated into inflammation. The hazy vision which accompanies this con dition is partly attributable to this cause ; but more frequently depends on the im perfect removal of the lachrymal secretion, which becomes irregularly diffused in a more or less solid or dried state over the globe. The general relaxation of the orbicularis perhaps aids this, and it has also the effect of altering the position of the punctalachrymalia, and thus preventing the natural exit of the secretion, which is sometimes poured down the face. But these effects are on the whole rarely so complete as is above stated ; the aperture between the eyelids is usually small, and movements of the globe of the eye are to some extent substituted for those of the lids ; so that the general results offer the most marked contrast to the rapid disorganization which follows the section of the fifth nerve which forms the sensitive supply of these parts.
Besides the influence of the facial nerve on mastication, as shown by the result of its paralysis or artificial division ; the sense of taste appears to be considerably impaired on the corresponding side. This fact has been well illustrated by M. Claude Bernard*, who has collected nine or ten cases of this kind. The manner in which the sense is affected seems to vary. Thus, he describes it as an impairment, in which the most sapid sub stances failed to excite their ordinary im pressions, and are only perceived after a c onsiderable interval of time. Professor Roux has left a recital of his sensations during a rheumatic facial hemiplegia ; and in his description, which Longet quotes ±, he mentions that everything on the affected side tasted strongly metallic ; whence it would appear that this diminution of taste is some times substituted by a perversion or deprava tion of the function.