460 EDWAED B. POULTON. 



These tactile end organs are very common beneath the epi- 

 thelium of the lower surface of the tip, and are rarely found 

 between the papillae of the upper surface of this subregion. 

 They do not occur in any other part of the tongue, and are 

 not found in the posterior papillae of this subregion where the 

 cornified layer is much developed and the functions are purely 

 mechanical. They disappear about 4 mm. from the posterior 

 limits of the anterior subregion. 



It is very probable that there are also nerve endings in the 

 epithelium of the papillae, for it is very common to see fibres 

 continued from the mucous membrane into the epithelium, 

 especially at the apex of a secondary papillary process. If 

 these fibres are nervous (which cannot certainly be made out 

 in this specimen) they are probably bundles of primitive fibrils. 

 Blood-vessels are very abundant in the tactile papillae. 



B. The Posterior Subregion. — The transition between 

 this part of the tongue and that just described is shown in fig. 

 6. It is seen that the rasping papillae are continuous from the 

 one on to the other without any change of structure except an 

 increase in thickness of the corneous epithelium. The gland 

 tubes where present open between, never on, the papillae, and 

 are wider just before they perforate the epithelium than is the 

 case anteriorly. No tactile end organs appear to be present, 

 and the functions of this subregion must be exclusively 

 mechanical. Between the widely separated papillae already 

 described, occur abundant simple pointed papillae (figs. 6 and 7), 

 which are usually much worn down. In all the points men- 

 tioned there are traces of a transition from the anterior to the 

 posterior subregion, but a distinct difference between the two 

 is seen in the structure of the epithelial layer. At the point 

 of contact the epithelium of this subregion forms a thinner 

 layer (fig. 6), and this is also true of all other parts of the 

 tongue where there is a similar change of structure. This 

 fact only holds for the contact, since there may be great varia- 

 tion in the thickness of both kinds of epithelium distally to 

 this point. The structural difference is of greater importance, 

 and can be detected even in an unstained section of the tongue 



