-4G2 EDWARD B. POULTON. 



2, and tlie deeply stained cells above^ coalesce and disappear 

 after persisting for a short distance (fig, 6). 



The oral mucous membrane which is continuous with the 

 sides of this part of the tongue, has a very thick simple epithe- 

 lium with fine papillae. 



The overhanging surface is almost identical in structure 

 with the rest of the subregion with which it is continuous, and 

 the papillse are of the same structure. The rasp-like papillae 

 on the horizontal surface are directed backwards, and these 

 being continuous on to the overhanging surface (which is 

 directed forwards at an acute angle) are there directed for- 

 wards. Hence in antero-posterior movement of one surftice 

 upon the other these papillte would work in opposite directions 

 and would form very efficient agents of attrition, being greatly 

 aided by the very numerous pointed papilla?. That this is the 

 true function of the subregion is rendered likely by the 

 situation of these two surfaces at the level of the four most 

 effective teeth. The food after being crushed by the teeth 

 would be forced inwards and further rubbed down between 

 these surfaces, the two horny tooth-like papillse no doubt 

 assisting in the operation by friction against the horizontal 

 surface below. The greater thickness of tlie epithelium on the 

 overhanging surface is doubtless due to the greater length of 

 horizontal surface rubbed against it. 



In favour of this view of the action of the subregion is the 

 great wear shown by the epithelial surface and the papillae 

 (especially the more numerous simple pointed ones) ; and the 

 fact that the two surfaces are almost apposed in a tongue pre- 

 served in the Oxford Museum, while the horny teeth were 

 directed downwards towards the surface beneath. In another 

 •specimen which I was enabled to examine through the kind- 

 ness of Professor Moseley, the teeth were almost in contact 

 with the horizontal surface below, while in this also the over- 

 hanging and horizontal surfaces were nearly apposed. It is 

 probable that the chisel-like summits assist in scraping off 

 particles that are entangled among the papillse. The teeth 

 and anterior part of the horizontal surface may also be rubbed 



