THE SPECIAL SENSES 277 



muscles composing it being so numerous and interwoven as to 

 give it the freedom and variety of motion which it possesses. 

 It can curve itself upward or downward ; it can extend or con- 

 tract itself; and, with its point, can sweep the cavity of the 

 mouth, in all directions, in the search for scattered particles of 

 food. 



30. The upper surface of the tongue is peculiar, being 

 marked by the presence of innumerable papillae, some of which 

 are of microscopic size, resembling those that abound in the 

 lingers, and in other parts of the body that have the sense of 

 touch. Others are much larger, and give to the tongue its 

 roughness of feeling and appearance. Through the medium 

 of these papillae, the tongue receives impressions of touch and 

 temperature, as well as taste : indeed, its extremity is fully as 

 delicate, in respect to tactile sensations, as the tips of the fin- 

 gers themselves. It can recognize the two points of the com- 

 passes when separated not more than one twenty-fourth of an 

 inch ; the back of it is much less sensitive to touch, while at 

 the same time it is more highly sensitive to impression of 

 taste. . 



31. Each lateral half of the tongue resembles the other in 

 structure, and each receives- the same number of nerves 

 three. One of these regulates motion, the other two are nerves 

 of special sense. One of the latter supplies the front half 

 of the tongue, and is called the gustatory nerve. This is a 

 branch of the great cranial nerve, called the " fifth pair," which 

 ramifies in all parts of the face. The back of the tongue is 

 endowed with the power of taste, -through a nerve known as 

 the glosso-pharyngeal, because it is distributed both to the 

 tongue and throat. This difference in the nervous supply of 

 the tongue becomes significant, when we learn, as we shall 

 presently, that each part of it perceives a different class of 

 flavors. 



32. The Sense of Taste. Taste is the special sense by means 



30. Peculiarities of the tongue ? Uses of the papillae ? 



31. Resemblance in the parts of the tongue ? Powers and functions of the parts ? 



32. Taste? What are the requisites to taste ? 



