4SS THE SPECIAL SENSES. 



by organic disease, before its emergence from the stylo-mastoid 

 foramen, not only is there a paralysis of the superficial muscles of 

 the face, but the sense of taste is diminished on the corresponding 

 side of the tongue. If the tongue be protruded, and salt, citric acid 

 or sulphate of quinine be placed upon its surface on the two sides 

 of the median line, the taste of these substances is perceived on the 

 affected side more slowly and obscurely than on the other. It is 

 not, therefore, a destruction, but only a diminution of the sense of 

 taste, which follows paralysis of the facial in these instances. At 

 the same time the general tactile sensibility of the tongue is unal- 

 tered, retaining its natural acuteness on both sides of the tongue. 



The exact mechanism of this peculiar influence of the facial nerve 

 upon the sense of taste is not perfectly understood. It may be 

 considered as certain, however, that it is derived through the 

 medium of that branch of the facial nerve known as the chorda 

 tympani. This filament leaves the facial at the intumescentia 

 gangliformis, in the^interior of the aqueduct of Fallopius, enters the 

 cavity of the tympanum, passes across the membrane of the tym- 

 panum, and then, emerging from the cranium, runs downward and 

 forward and joins the lingual branch of the fifth pair. It then ac- 

 companies this nerve as far as the posterior extremity of the sub- 

 maxillary gland. Here it divides into two portions ; one of which 

 passes to the subm axillary ganglion, and, through it, to the sub- 

 stance of the submaxillary gland, while the other continues onward, 

 still in connection with the lingual branch of the fifth pair, and, in 

 company with the filaments of this nerve, is distributed to the tongue. 



The chorda tympani thus forms the only anatomical connection 

 between the facial nerve and the anterior part of the tongue. When 

 the facial, accordingly, is divided or injured after its emergence 

 from the stylo-mastoid foramen, no effect is produced upon the 

 sense of taste; but when it is injured during its course through the 

 aqueduct of Fallopius, and before it has given off the chorda tym- 

 pani, this nerve suffers at the same time, and the sense of taste is 

 diminished in activity, as above described. It is probable that this 

 affect is produced in an indirect way, by a diminution in the activity 

 of secretion in the lingual follicles, or by some alteration in the 

 vascularity of the parts. 



SMELL. The main peculiarity of the sense of smell consists in 

 the fact that it gives us intelligence of the physical character of 

 bodies in a gaseous or vaporous condition. Thus we are enabled to 



