250 



THE DIGESTIVE ORGANS. 



surface. The whole structure is surrounded by the epithelium of 

 the mucous membrane of the regions in which they occur, except 

 at the attenuated outer end of the taste-bud, where, by means of a 

 small opening, the taste-pore, it communicates with the oral cav- 

 ity. Most of the cells constituting the taste-buds are elongated, 

 spindle-shaped structures, extending from one end of the organ to 

 the other, with spaces between them. There are four varieties of 

 these cells : (i) The outer sustentacular or tegmental cells, lying at 

 the periphery of the organ with a nucleus in their center, and 

 having a short, cone-shaped cuticular projection ; (2) the inner 

 sustentacular or rod-shaped cells, which are more slender structures 

 with basally situated nuclei and without a cuticular projection ; 

 between the latter are (3) elongated, spindle-shaped, neuro-epithe- 



Groove sur- 

 rounding 

 papilla. 



Fig. 194. Longitudinal section of a human circumvallate papilla; X 2O - 



lial cells, with the nucleus of each in the thickest portion of the 

 cell, and with slender, stiff processes projecting into the taste-pore ; 

 (4) a few broad basal cells, communicating with each other as well 

 as with the sustentacular cells by numerous processes. We have, 

 therefore, in the cells of the first, second, and probably fourth 

 varieties, elements which belong exclusively to the sustentacular 

 apparatus of the organ (Hermann, 85, 88). 



Von Ebner found in the taste-buds of the circumvallate papillae 

 of man, monkey, and cat, as well as of the papillae foliatae of the 

 rabbit, an open space situated between the taste-pore and the tip 

 of the taste-bud (Fig. 195). These spaces vary according to the 

 species, and are bounded above by the summits of the tegmental 

 cells and laterally and below by the more centrally situated sus- 



