808 



THE TONGUE, 



When examined microscopically in sections, all the kinds of papillee now 

 described are observed to be bearers of closely set secondary papillae. The 

 secondary papillae are the structures which correspond with the papillae of 

 the general integument, and are occupied each by a long loop of capillary 

 blood-vessel. Simple papillae of the same description are likewise inter- 

 spersed between the three large kinds, and are found on the back part of 



Fig. 566. Two FILIFORM PAPILLAE, 

 ONE WITH EPITHELIUM, THE OTHER 

 WITHOUT (from Kolliker, after 

 Todd and Bowman). ^ 



p, the substance of the papillae di- 

 viding at their upper extremities into 

 secondary papillae ; a, artery, and v, 

 vein, dividing into capillary loops ; 

 e, epithelial covering, laminated be- 

 tween the papillae, but extended into 

 hair-like processes /, from the ex- 

 tremities of the secondary papillae. 



the tongue, behind the circum- 

 vallate range, as well as covering 

 the under surface of the tongue 

 and the rest of the mucous mem- 

 brane of the mouth. The epi- 

 thelium covering the tongue, 

 like that of the mouth generally, 

 is of the squamous kind. It is 

 of considerable thickness, and 

 the simple papillae, together with 

 the secondary papillae surmount- 

 ing those of the circumvallate 

 and fungiform kinds, are con- 

 cealed beneath it, or nearly so. 

 But the secondary papillae, borne 

 by those of the filiform kind, 

 are peculiar both in contain- 

 ing a number of elastic fibres, 



which give them greater firmness, and in the character of their epithelial 

 covering, which is dense and imbricated, and which forms a separate process 

 over each, greater in length than the papilla which it covers. Over some 

 of the filiform papilla these processes form a pencil of fine fibres ; and on 

 others they approach closely in character and structure to hairs. The papillae 

 are undoubtedly the parts chiefly concerned in the special sense of taste ; 

 but they also possess, in a very acute degree, common tactile sensibility ; 

 and the filiform papillae, armed with their denser epithelial covering, serve 

 a mechanical use, in the action of the tongue upon the food, as is well 

 illustrated by the more developed form which these papillae attain in many 

 carnivorous animals. The papillary surface of the tongue is supplied abun- 

 dantly with nerves. It is difficult to trace the nerve- fibres in the papillae 

 filiformes, owing to the presence of elastic filaments. In the papillae fungi- 

 formes the nerves are larger and more numerous, and form a plexus with 

 brush- like branches : but they are still more abundant, and of greater size 

 in the papillae circumvallatae. 



Little that is satisfactory is known of the mode of termination of the 



