CHAP, xv.] MUCOUS MEMBRANE OF THE TONGUE. 435 



surface, like the villi of the intestinal tube, occasioning the familiar 

 roughness of the tongue. This, however, is to be taken with the 

 limitations hereafter to be detailed. 



The epithelium of the tongue is of the scaly variety, and in this 

 respect resembles the cuticle. Like the cuticle, also, it undergoes 

 certain modifications in its mode of aggregation in different localities. 

 In general it is much thinner than in the skin, so that the intervals 

 between the large papillae are not filled up by it, but each has a 

 separate investment, from root to summit. The continuity of the 

 epidermis over the whole organ admits of easy demonstration by 

 maceration, or boiling ; by which it is detached entire, bearing the 

 print of the surface below, on which it has been moulded. The 

 deeper epithelial particles may sometimes be detached as a separate 

 sheet, corresponding to the so-called rete mucosum; but these par- 

 ticles never contain colouring matter. In animals which have the 

 epithelium of the tongue much thicker than in man, it admits of 

 being separated with care into a great many layers, at the will of 

 the anatomist. The density of the epithelium is evidently a pro- 

 vision to defend the invested structure from the bad effects of the 

 pressure and friction to which they are exposed during mastication, 

 and hence it is greatest about the middle of the upper surface of 

 the organ. It is here that the " fur" usually accumulates most in 

 disease, being, in fact, no other than a depraved and overabundant 

 formation of the epithelium. 



Three principal varieties si papilla are visible with the naked eye 

 on the dorsal aspect of the tongue. These are, 1, the circumval- 

 late or calyciform, eight or ten in number, situated in a V-shaped 

 line at the base of the organ (fig. 94, a) ; the fungiform, scattered 

 over the surface, especially in front of the circumvallate, and about 

 the sides and apex, b ; and the conical or filiform, much the most 

 numerous, studding most of the surface, though most largely deve- 

 loped in the central part, d. These three varieties will require a 

 separate description; they are very distinct from one another if 

 well-marked specimens are selected ; but, as might be expected, 

 there are many intermediate forms by which they seem to run 

 imperceptibly into one another. We may premise, however, with 

 regard to them all, that although they appear to have been hitherto 

 regarded as simple papillae, analogous to, though larger than, those 

 of the skin, yet we have found them to be compound organs, clothed 

 with secondary, simple, and much more minute papillae, concealed 

 under the epithelial investment, and scarcely or not at all visible 

 until this covering is removed. 



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