THE GUSTATORY ORGANS 133 



membrane is raised above the general level (vallum) (fig. 159). These 

 papillae form a V-shaped line towards the back of the tongue ; they 

 receive filaments of the glosso-pharyngeal nerve, and have taste-buds in 

 the epithelium which covers their sides, and in that of the side of the 

 vallum. They are known as the circumvallate papilla. (2) All the rest 

 of the papillary surface of the tongue is covered by conical papilla, so 

 named from the conical pointed cap of epithelium which is borne by 

 each ; sometimes this cap is fringed with fine epithelial filaments, when 

 they are termed filiform (fig. 161). (3) Scattered here and there 

 amongst the conical papillae are other larger papilla?, the fungiform 

 (fig. 160). These are very vascular, and lie partly embedded in little 

 depressions of the mucous membrane. 



Small tubular glands may be seen between the superficial muscular 

 fibres sending their ducts to the surface. Most of them secrete mucus, 

 but those which open into the trenches of the circumvallate papillae, 

 and a few others elsewhere, yield a serous secretion. 



The mucous membrane at the back of the tongue contains a large 

 amount of lymphoid tissue. 



The taste-buds. The minute gustatory organs which are known as 

 taste-buds may be seen in sections which pass through the papillae 

 vallatae or the papilla fungiformes ; they are also present here and 

 there in the epithelium of the general mucous membrane of the tongue, 

 especially at the back and sides, and occur also upon the under surface 

 of the soft palate, and on the epiglottis. But they are most easily 

 studied in the papillae foliatae of the rabbit, two small oval areas lying 



FIG. 162. TONGUE OF RABBIT, SHOWING THE SITUATION OF THE 



PAPILLAE FOLIAT^E, p. 



on either side of the back of the tongue and marked transversely with 

 a number of small ridges or laminae with intervening furrows (see 

 figs. 162 and 163). Sections across the ridges show numerous 

 taste-buds embedded in the thick epithelium which clothes their sides. 

 The taste-buds are ovoid clusters of epithelium-cells which lie in 

 cavities in the stratified epithelium (fig. 164). The base of the taste- 

 bud rests upon the corium of the mucous membrane, and receives a 

 branch of the glosso-pharyngeal nerve ; the apex is narrow and coin- 



