SENSE OF TASTE. 211 



3. The circumuallate papilla are rounded eminences from eight to ten in 

 number, situated at the base of the tongue, where they form a V-shaped 

 figure. They are quite large, and consist of a central projection of mucous 

 membrane, surrounded by a wall, or circumvallation, from which they 

 derive their name. 



The taste-beakers, supposed to be the true organs of taste, are flask-like 

 bodies, ovoid in form, about ^ of an inch in length, situated in the epithelial 

 covering of the mucous membrane, on the circumvallate papillae. They con- 

 sist of a number of fusiform, narrow cells, which are curved so as to form 

 the walls of this flask-like body; in the interior are elongated cells, with large, 

 clear nuclei, the taste-cells. 



Nerves of Taste. The chorda tympani nerve, a branch of the facial, 

 after leaving the cavity of the tympanum, joins the third division of the fifth 

 nerve between the two pterygoid muscles, and then passes forward in the 

 lingual branches, to be distributed to the mucous membrane of the anterior 

 two thirds of the tongue. Division or disease of this nerve is followed by a 

 loss of taste in the part to which it is distributed. 



The glossopharyngeal enters the tongue at the posterior border of the 

 hyoglossus muscle, and is distributed to the mucous membrane of the base and 

 sides of the tongue, fauces, etc. 



The lingual branch of the tri-geminal nerve endows the tongue with general 

 sensibility; the hypoglossal endows it with motion. 



The nerves of taste in the superficial layer of the mucous membrane form 

 a fine plexus, from which branches pass to the epithelium and penetrate it; 

 others enter the taste-beakers, and are directly connected with the taste-cells. 



The seat of the sense of taste has been shown by experiment to be the whole 

 of the mucous membrane over the dorsum of the tongue, soft palate, fauces, 

 and upper part of the pharynx. 



The sense of taste enables us to distinguish the savor of substances intro- 

 duced into the mouth, which faculty is different from tactile sensibility. The 

 sapid qualities of substances appreciated by the tongue are designated as bit- 

 ter, sweet, alkaline, sour, salt, etc. 



The essential conditions for the production of the impressions of taste 

 are: 



1. A state of solubility of the food. 



2. A free secretion of the saliva, and 



3. Active movements on the part of the tongue, exciting pressure against 

 the roof of the mouth, gums, etc., thus aiding the solution of various articles 

 and their osmosis into the lingual papillae. 



