640 



THE SENSES 



The mucous membrane in the regions just mentioned possesses special 

 epithelial structures called taste buds. The taste buds are very abundant 

 in the side walls of the circumvallate papillae. They are also present in the 

 fungiform papillae, in the foliate papillae, and in the mucous membrane. 

 The taste bud is located at the deeper part of the stratified epithelium, is 

 ovoid in shape, and its free end abuts on the surface or opens to the surface 

 by a short canal. It is composed of two kinds of modified epithelial cells 

 the supporting cells, which are long, spindle-shaped cells that form a sheath 

 around the special gustatory cells; and the taste cells, which are neuro-epithe- 

 lial cells that are found in the center of the taste bud. They are very slender 

 cells that project on the surface by a delicate process. A bundle of nerve 

 fibrils enters the base of each taste bud and forms a net about the taste cells. 



FIG. 423. 



FIG. 424. 



FIG. 423. Taste Bud from Side Wall of Circumvallate Papillee. (Merkel-Henle.) 

 a, Taste pore; b, nerve fibers, some of which enter the taste bud, intrageminal fibers, while 

 others end freely in the surrounding epithelium, intergeminal fibers. 



FIG. 424. Vertical Section of a Circumvallate Papilla of the Calf, i and 3, Epithelial 

 layers covering it; 2, taste goblets; 4, and 4', duct of serous gland opening out into the pit 

 in which the papilla is situated; 5 and 6, nerves ramifying within the papilla. (Engelmann.) 



The circumvallate, the fungiform, and the filiform papillae, shown in 

 figure 422, are special structures that facilitate the stimulation of the taste 

 buds by sapid substances. They are all formed by a projection of the 

 mucous membrane, and contain special branches of blood vessels and 

 nerves. In details of structure, however, they differ considerably one from 

 another. 



Circumvallate Papillee. These papillae, figure 424, eight or ten in number, 

 are situated in two V-shaped lines on the base of the tongue. They are 

 circular elevations from i to 2 mm. in diameter each, with a central depres- 

 sion, and surrounded by a circular fissure, at the outside of which is a slightly 

 elevated ring. Both the central elevation and the ring are formed of close 

 set simple papillae. 



