600 THE SENSES. 



Each organ of special sense consists First, of a nerve, endowed with 

 the special sensibilitj' required for its peculiar function ; and, Secondly, 

 of certain accessory parts, forming an apparatus adapted to aid in the 

 performance of this function, and render it more delicate and complete. 



Sense of Taste. 



The sense of taste is, in some measure, intermediate in character 

 between the functions of general and special sensibility. First, the 

 organ by which it is exercised forms a part of the mucous membrane 

 lining the commencement of the alimentary canal, furnished with vas- 

 cular and nervous papillae analogous in structure to those of the general 

 integument. Secondly, this mucous membrane is also endowed with 

 general sensibility. Although it is highly probable that certain minute 

 formations in its epithelial layer, known as " taste buds," may be espe- 

 cially connected with the perception of savors, there is thus far no cer- 

 tainty in this respect ; and in any case the tactile and gustatory sensi- 

 bilities are closely intermingled in the substance of the mucous mem- 

 brane. Thirdly, the sensibility of taste is not confined to the fibres of 

 one special and distinct nerve, but resides in portions of two, namely, 

 the lingual branch of the fifth pair and the glossopharyngeal nerve, 

 which also supply general sensibility to the corresponding parts. 

 Fourthly, this sense gives rise to impressions only from the actual con- 

 tact of sapid substances with the mucous membrane, and can establish 

 no communication with objects at a distance ; and Fifthly, though some 

 of the impressions derived from this source are of a distinct and special 

 character, others, like the taste of oily or mucilaginous substances, differ 

 but little in kind from those of tactile sensibility. 



The sense of taste is localized in the mucous membrane of the tongue, 

 the soft palate, and the pillars of the fauces. The tongue, which is more 

 particularly the seat of this sense, is a flattened, leaf-like muscular organ, 

 attached to the inner surface of the symphysis of the lower jaw in front, 

 and to the os hyoides behind. It has a vertical sheet or lamina of fibrous 

 tissue in the median line which serves as its framework, and is provided 

 with longitudinal, transverse, and radiating muscular fibres, by which it 

 can be elongated, retracted, and moved in every direction. 



The mucous membrane of the fauces and posterior third of the tongue, 

 like that lining the cavity of the mouth, is covered with vascular papillae, 

 analogous in structure to those of the skin, but imbedded and concealed 

 in the smooth layer of epithelium forming the surface of the organ. 

 Upon the dorsum of the tongue, about the junction of its posterior and 

 middle thirds, there is a double row of rounded eminences, arranged in 

 a V-shaped figure, running forward and outward, on each side, from the 

 situation of the foramen caecum ; and from this point forward, the 

 mucous membrane is covered with thickly-set papillae, containing nerves 

 and bloodvessels, and giving a soft velvety texture to the surface of the 

 organ. 



The lingual papillae are of three different kinds. First i\\Q filiform 



