THE ORGANS OF TASTE. 



327 



often terminates in a depression, closed at the bottom, which is called 

 i\\Q foramen ccccum (Morgagni), and in which several nmcou^ glands o-^en. 

 Three folds, named the glosso-epiglottic folds or frasnula, of which the 

 middle one is the largest (frffinum epiglottidis), pass backwards from 

 the base of the tongue to the epiglottis. The upper surface of the 

 tongue in front of the foramen caecum (the anterior two-thirds) is covered 

 with small eminences named inqnlUc. They are found also upon the 

 tip and borders, where, however, they gradually become smaller, and 

 towards its under surface they disappear. These papilla are dis- 

 tinguished into three orders, circumvallate, fungiform and filiform, vary- 

 ing both in size and form, but all of them visible to the naked eye ; they 

 themselves, like the res>t of the mucous membrane of the tongue and 

 mouth generally are covered with closely set, microscopic secondary 

 papillce hidden under the epithelium, which correspond with those of the 

 skin, and are each occupied by a long loop of capillaiy blood-vessels. 



The large circumvallate papillae (fig. 226, 1, 2), from seven to twelve 

 in number, are ibund on the back part of the tongue, arranged in 



They are situated in cup-like 



Fig. 227. — Vertical Section of Cir- 

 cumvallate Papilla from the 

 Calf (Engelmann). 25 Diameters. 



A, the papilla ; B, the surrounding 

 wall. The figure shows the nerves of 

 the papilla sjDreading towards the sur- 

 face, and towards the taste-buds which 

 are imbedded in the ei)ithelium at the 

 sides ; in the sulcus on the left the duct 

 of a gland is seen to open. 



two rows, which run obliquely 



backwards and inwards, and 



meet towards the foramen cte- 



cum, like the arms of the letter V. 



depressions of the mucous membrane, and have the shape of a trun- 

 cated cone, of which the 

 ^^s- 228. smaller end is attached 



to the bottom of the 

 cavity, and the broad flat- 

 tened base appears on the 

 surface (fig. 227). They 

 are therefore surrounded 

 by a circular trench (fos- 

 sa), around which again 

 is an annular elevation of 

 the raucous membrane 

 {vallum), and in some of 

 them there is found a cen- 

 tral depression, into which 

 the ducts of one or more 

 glands open. The epithe- 

 lium covering the papillae 



vallatas is thick and stratified, as elsewhere in the mouth, and completely 



conceals the minute secondary papillae. Forming a zone around the sides 



of the papilla are found, imbedded in this thick epithelium, peculiar 



Fig. 228. — Two Taste-buds from the Papilla 

 FoLiATA OF THE Eabbit. 450 DiAMETERS (Engel- 

 mann). 



