482 THE SPECIAL SENSES. 



Secondly, it gives us impressions of such substances only as are 

 actually in contact with sensitive surfaces, and can establish no 

 communication with objects at a distance. Thirdly, the surfaces 

 which exercise the sense of taste are also endowed with general sen- 

 sibility; and Fourthly, there is no one special and distinct nerve 

 of taste, but this property resides in portions of two different 

 nerves, viz., the fifth pair and the glosso-pharyngeal ; nerves which 

 also supply general sensibility to the mouth and surrounding parts. 

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

 tongue, the soft palate, and 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 a 

 framework, and is provided with an abundance of longitudinal 

 transverse and radiating muscular fibres, by which it can be elon- 

 gated, retracted, and moved about 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 

 minute vascular papillae, similar to those of the skin, which are, 

 however, imbedded and concealed in the smooth layer of epithe- 

 lium forming the surface of the organ. But about the junction of 

 its posterior and middle thirds, there is, upon the dorsum of the 

 tongue, a double row of rounded eminences, arranged in a V-shaped 

 figure, running forward and outward, on each side, from the situa- 

 tion of the foramen caecum ; and, from this point forward, the upper 

 surface of the organ is everywhere covered with an abundance of 

 thickly-set, highly developed papillae, projecting from its surface, 

 and readily visible to the naked eye. 



These lingual papillae are naturally divided into three different 

 sets or kinds. First, the filiform papillse, which are the most nume- 

 rous, and which cover most uniformly the upper surface of the 

 organ. They are long and slender, and are covered with a some- 

 what horny epithelium, usually prolonged at their free extremity 

 into a filamentous tuft. At the edges of the tongue these papillae 

 are often united into parallel ranges or ridges of the mucous mem- 

 brane. Secondly, the fungiform papillae. These are thicker and 

 larger than the others, of a rounded club-shaped figure, and covered 

 with soft, permeable epithelium. They are most abundant at the 

 tip of the tongue, but may be seen elsewhere on the surface of the 

 organ, scattered among the filiform papillae. Thirdly, the circum- 



