TONGUE OF ORNITHORHYNCUUS PARADOXUS. 463 



against the roof of the mouth, -which here is very dense and 

 presents transverse curved ridges. No glands open upon the 

 overhanging surface. In working at this surface a singularly 

 difficult structure was met with which I mention, as it seems 

 likely that others might have a similar experience. At one 

 point only, a series of specimens showed successive oblique 

 sections of a single hair which penetrated to the mucous mem- 

 brane. The epithelium round it was much modified by the 

 presence of the hair, so that it was long before I could be sure 

 that the structure was accidental. A hair (probably one of the 

 animal's) must have been arrested at this surface and the end 

 become inserted in some slight cavity between the cells. Thus 

 the hair gradually worked through the whole thickness of the 

 epithelium. It was very interesting to note that the super- 

 ficial epithelial layer (4) was cornified for a considerable distance 

 round the foreign object and due to its presence. There was a 

 hollow at the surface filled with fragments of foreign objects, 

 and probably partially derived from the hair itself. The con- 

 tour of the hair was rough and frayed where it passed through 

 the epithelium, and most of its course was greatly twisted. 

 These were indications of its gradual passage along lines of 

 least resistance, and of the great friction caused. 



The two horny teeth which form the boundary between the 

 anterior and posterior regions (here classified with the former') 

 are covered, except at their apices, with a thick layer of corni- 

 fied cells (fig. 7). These cells are, however, different from those 

 of the corneous layer (3) of the overhanging and other sur- 

 faces, the difference being especially seen in their behaviour 

 with logwood. The peculiarity belongs to the latter, and the 

 superficial cells of the horny teeth are normal cornified cells. 

 Towards the apex a few large rounded deeply staining cells are 

 sometimes seen in the cornified layer. They may represent 

 isolated unaltered cells continued from the layers below, as 

 they are sometimes seen in lines extending from the apex of a 

 papillary process. I do not feel certain as to their correct 

 interpretation. 



The layer beneath is made up of very granular polygonal 



