498 THE SOLIDS. 



cup, are closely set with very many simple papillae, which are 

 short, obtuse, and dilated at their extremities. A calyciform 

 papilla, perfectly freed from epithelium, and with all the 

 secondary papillae visible, forms a very beautiful object. (See 

 Plate LXVI. fig. 1.) 



The foramen ccecum usually contains one and sometimes 

 two large papilla, similarly clothed with secondary papillae, 

 and according as it includes one or two papilla, it is to be 

 regarded as a single or double modified calyciform papilla. 



In front of the calyciform papillae, in some tongues, a 

 number of large and irregular papilla exist, invested with 

 secondary papillae similar to those of the calyciform papillae, 

 but not, like the latter, seated in cups. 



On the edges and under surface of the tongue numerous 

 mucous follicles are observed : it is sometimes, however, diffi- 

 cult to distinguish between these and simple papillae, in 

 consequence of the latter being frequently perforated in the 

 centre, and thus combining the characters of both follicles 

 and papillae. (See Plate LXV. figs. 1, 2, 3.) 



The epithelial investment of the tongue adheres very 

 closely to the papillae, and generally requires one or two 

 weeks' maceration for its complete removal; even then, in 

 but few instances in the human subject, can it be removed in 

 entire pieces, it in most cases crumbling away into its con- 

 stituent cells. 



It adapts itself accurately to the papillary structure of the 

 tongue, and is of sufficient thickness to conceal effectually 

 the simple papillae, whether these exist by themselves or con- 

 stitute by their aggregation the compound papillae. For the 

 satisfactory study of the papillae, therefore, it is absolutely 

 necessary that the epithelium should be entirely removed. 



The epithelium of the tongue presents all the characters of 

 the epidermis of the skin, consisting, like it, of numerous 

 layers of large and nucleated cells, those forming the outer 

 layers being flattened and membranous, while the deeper-seated 

 cells are rounded and granular. (See Plate LXV. fig. 6.) 



The thickness of the epithelium of the tongue in the human 

 subject varies very considerably in different cases, and would 



