THE MOUTH AND TONGUE. 383 



the following differences of appearance : their epithelial cover- 

 ing is thicker, and stratified somewhat after the manner of the 

 filiform papillse, the taste-goblets are absent upon their sur- 

 face, and the nerve-fibres, so far as they can be traced, termi- 

 nate in bulbs. 



The circumvallate papilla, about nine in number, are situ- 

 ated at the back part of the tongue. They form an irregular 

 row on each side and incline slightly from before backward 

 toward the median line. At their point of junction is t\\Q fora- 

 men ccecum of Morgagni. Each circumvallate papilla consists 

 of a broad, flat elevation of the mucous membrane, which is 

 surrounded with a fossa. Its surface is covered with small 

 secondary papillse, and the epithelium is like that of the 

 fungiform papillse. Taste-goblets are found abundantly upon 

 the lateral edges and toward the centre of the papillse. The 

 blood-vessels are arranged as in the fungiform papillse, and 

 each secondary papilla contains a vascular loop. The nerves 

 are derived from the glossopharyngeal. They consist of single 

 pale nerve-fibres, which form a network in the centre of the 

 papillae and ascend toward its peripheral surface. 



The papilla foliatce, or fimbrise linguae, consist of several 

 folds of the mucous membrane at the lateral edges of the 

 tongue. Between them are scattered a few fungiform papil- 

 lse, and they contain a considerable number of taste-goblets. 

 Many excretory ducts of acinous glands empty at the bases of 

 these folds. 



The sublingual mucous membrane includes that of the floor 

 of the mouth. Both are of the same structure, and pass into 

 each other by means of a reduplication, the frsenum linguse. 



The secreting glands of the root of the tongue are of two 

 varieties serous and mucous. The mucous glands are like 

 those elswhere in the buccal cavity. Their ducts are some- 

 times lined with ciliated epithelium. The glands themselves 

 are not found in the neighborhood of the taste-goblets. The 

 serous glands, on the other hand, are found most abundantly 

 in those parts of the tongue which are most richly supplied 

 with taste-goblets. Their ducts open into the grooves which 

 are lined by the taste-goblets. 



The follicular glands, which form the collections of adenoid 

 tissue found at the base and at the sides of the tongue, are not 

 true glands, but rather elevations of the mucous membrane 



