THE SENSE ORGANS 



405 



Pharyngeal taste-buds occur in larval cyclostomes, while in the adult 

 they are present also on the surface of the head. In elasmobranchs the 

 taste-buds are limited to the lining of the mouth and pharynx, chiefly 

 on the surface of papillae. In ganoids and teleosts they are found on the 

 surface of the head as well as on the pharynx. A few teleosts such as 

 Ameiurus have taste buds on the surface of the trunk, fins, and mouth. 



In Amphibia, with the assumption of a land life, taste-buds become 

 limited to the tongue and the roof of the mouth. In man, they are found 



EPIGLOTTIS. 



FOLIATE 

 PAPILLAE 



FiG- 357- — The dorsal surface of the tongue. The sulcus terminalis divides the 

 body or apex of the tongue from the root. The two regions have a different embryonic 

 origin. (Redrawn after Sobotta.) 



on the tongue, especially on the sides of the vallate papillae, upon the soft 

 palate, and upon the posterior surface of the epiglottis. 



A taste-bud is an ovoid cluster of columnar epithelial cells, each of 

 which extends from the basement membrane to the free surface of the 

 epithelium. The cells of the peripheral layer are arranged like sections of a 

 melon, so that the ends of the cells are brought close together around a 

 small pore which opens on the surface. Two kinds of cells are differen- 

 tiated, peripheral supporting cells, and sensory taste cells which form 

 the core. The sensory cells stain more intensely, and are distinguished 

 by the bristle-like process in which each cell terminates. (Fig. 84) 



