676 



TEXT-BOOK OF PHYSIOLOGY 



which is uncertain. From these nuclei axons arise which in all probability 

 cross the median plane and ascend to the sub-collateral convolution. The 

 exact course of this gustatory tract is, however, obscure. 



The Tongue. The tongue consists of both intrinsic and extrinsic mus- 

 cles, in virtue of which it is susceptible of a change both in shape and in 

 position. The movements of the tongue, though not essential to taste, are 

 made use of in the finer discrimination of tastes. 



The tongue is covered over by mucous membrane continuous with that 

 lining the oral cavity. The dorsum of the tongue presents a series of papillae 

 richly supplied with blood-vessels and nerves. Of these there are three 

 varieties, the filiform, the fungiform, and the circumvallate. 



1. The filiform papilla, the most numerous, cover the anterior two-thirds of 



the tongue; they are conical or filiform in shape and covered with 

 horny epithelium which is often prolonged into filamentous tufts. 



2. The jungiform papilla, found chiefly at the tip and sides of the tongue, 



are less numerous but larger than the preceding and of a deep red 

 color. 



3. The circumvallate papilla, from eight to ten in number, are situated 



at the base of the tongue arranged in the form of the letter V. They 

 consist of a central projection surrounded by a wall or circumvallation 

 from which they take their name. 



The Peripheral End-organs. The Tastebuds. Embedded in the 

 epithelium covering the mucous membrane not only of the tongue but of 

 the palate and posterior surface of the epiglottis are small 

 ovoid bodies which from their relation to the gustatory 

 nerves are regarded as their peripheral end-organs and 

 known as taste-buds or taste-beakers. Each bud is ovoid 

 in shape (Fig. 285). Its base rests on the tunica propria; 

 its apex comes up to the epithelium, where it presents 

 a narrow funnel-shaped opening, the taste-pore. The 

 wall of the bud is composed of elongated curved epithe- 

 lium. The interior contains narrow spindle-shaped 

 neuro-epithelial cells provided at their outer extremity with 

 stiff hair-like filaments which project into the taste-pore. 

 The neuro-epithelial cells are in physiologic relation 

 with the nerves of taste. The terminal branches, after 

 entering the bud at its base, develop fine tufts which 

 come into contact with the cells. That the taste-buds 

 are connected with the nerves of taste is rendered prob- 

 able from the fact of their degeneration after division of 

 the nerves. 



The Taste Area. The taste area, though confined 

 for the most part to the tongue, extends in different in- 

 dividuals to the mucous membrane of the hard palate, 

 to the anterior surface of the soft palate, to the uvula, 

 the anterior and posterior half arches, the tonsils, the 

 posterior wall of the pharynx, and the epiglottis. 



The Taste Sensations. The sensations which arise in consequence of 

 impressions made by different substances on the peripheral apparatus of 

 this area are in so many instances combinations of taste, touch, temperature, 



FIG. 285. TASTE- 

 BUD FROM CIRCUM- 

 VALLATE PAPILLA OF 

 A CHILD. The oval 

 structure is limited to 

 the epithelium (e) 

 lining the furrow, 

 encroaching slightly 

 upon the adjacent 

 connective tissue (/); 

 o, taste-pore through 

 which the taste-cells 

 communicate with 

 the mucors surface. 

 (After Piersol.} 



