THE SENSE OF TASTE 



691 



evoke the sensations of taste. The specific physiologic stimulus is matter, 

 organic and inorganic, in a state of solution. 



The gustatory nerve as a distinct anatomic unit does not exist. The 

 fibers composing this nerve have for some unexplained reason become dis- 

 sociated and concealed partly in the nerve of Wrisberg, and its continua- 

 tion, the chorda tympani, and partly in the glosso-pharyngeal nerve. Had 

 this dissociation not taken place a thirteenth cranial nerve would have 

 been described. The nerves of taste contained in the trunks of the chorda 

 tympani (page 644) and of the glosso-pharyngeal (page 649) after entering 

 the medulla oblongata terminate around certain sensor end nuclei, the 

 exact location of 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 muscles, in virtue of which it is sus- 

 ceptible 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 papillae, 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 fila- 

 mentous 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 papillce, 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. 281). 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 epithelium. 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 



FIG. 282, 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 mucous surface. 

 (Ajter Piersol.) 



