Chemoreception 



455 



proper. In adult man the gustatory cells arc limited to the sides and top 

 of the tongue and to the epiglottis; in children they arc also present in the 

 cheeks. The tongue of man has four types of papillae: (1) Filiform papillae, 

 which are conical projections co\'ering the whole upper surface and tip and 

 borders of the tongue. These are not concerned in taste but are more highly 

 developed in cats, in which they are used as a rasp for cleaning meat from 

 bones. (2) Fungiform papillae, which resemble button mushrooms in shape, 



A 



Fig. 147. A, Diagram of a firimitive sensory neurone. B, Typical vertebrate sensory 

 neurone. The human olfactory neurones possess a peripheral cell body and resemble 

 the type shown in A. Human taste neurones possess a centrally located cell body and 

 resemble the type shown in B. After Cajar from Fulton.'"' 



are less numerous and are scattered ox'cr the front, upper surface. These 

 usually contain taste buds. (3) Circumvallate papillae, which are seven to 

 ten in number in man, are larger than the two previously mentioned, and 

 lie toward the back of the upper surface. Each papilla is a flat mound sur- 

 rounded by a groove forming a moat, both sides of which contain taste buds. 

 (4) Foliate papillae, xestigial in man, which form vertical ridges at the edge of 

 the back of the tongue. Each taste bud consists of a group of a dozen or more 

 elongated cells, some of which have minute hairlike processes. The taste 

 buds are embedded in the sides of the papillae, where they are sunk slightly 

 below the surface, and the opening of the small cavity which is thereby 

 formed is known as the gustatory pore. The hairlike processes of the sense 

 cells project through the pore into the cavity between the papillae. 



