1136 



TONGUE. 



Fig. 753. 



Epithelium of the tongue. 



a, a single flattened superficial cell, viewed super- 

 ficially and edgewise ; b, from the horse, showing 

 the filamentary prolongation of a part only of each 

 cell ; d, superficial ; c, deep layer. 



a small single circular nucleus may generally 

 be seen very plainly occupying a central posi- 

 tion in the cell, and unchanged in form and 

 size by any of the changes that the cell under- 

 goes. Certainly the epithelium, covering 

 most parts of the tongue, does not contain 

 any pigment ; but I think that covering the 

 filiform papillae in the centre of the dorsum 

 very frequently does ; and for these reasons, 

 because, first, the growth of the epithelium 

 here is very abundant, and it seems a general 

 rule that pigment should be associated with 

 an abundantly nourished or rapidly developed 

 epidermis, as is seen in hair, in the colour of 

 those spots that are called moles, and the hair 

 that proceeds from them, which, instead of being 

 invisible, as in neighbouring parts, is dark and 

 rank, and in the change of colour which the 

 cuticle and hair covering the parts of genera- 

 tion undergo at the increase of the nutrition 

 of the parts that accompanies the accession 

 of the generative function ; secondly, because 

 we see that the epithelium does undergo 

 great changes of colour, being generally dark- 

 est when most abundant ; thirdly, because, in 

 two cases that I have seen, in which the only 

 diseased condition was an enormous develop- 

 ment of the filiform processes which the epi- 

 thelium forms in the centre of the tongue, 

 the colour of the fur was a dark sepia or 

 Vandyke brown, almost black, exactly that 

 of pigment in other situations : we see too, 

 when the epithelium has been rendered 

 opaque by soaking the tongue in alcohol, that 

 all the other papillae are whiter than the fili- 

 form occupying the centre of the dorsum, 

 which retain their tawny colour. The epithe- 

 lium of the tongue differs from the dermic 

 cuticle chiefly in its moisture, and the delicacy 

 and softness of its structure. 



Papillary structure of the tongue. The pa- 

 pillae of the tongue are generally contrasted 

 with those of the skin, in that while the latter 

 are covered over with an even layer of epi- 

 derni's, and therefore not visible to the naked 

 eye, the latter stand out free from the surface 

 of the epithelium, dipping down between 

 them. But viewed by the light of recent 

 researches, this is seen to be only the appa- 

 rent difference, the real difference being that 

 while the papilla? of the skin are sessile, the 



papillae of the tongue are arranged in groups 

 on proper pedicles or supports, whose tops 

 and sides they cover, and which elevate them 

 above the general surface. For it has been 

 recently shown by Professors Todd and Bow- 

 man *, that the papillas, heretofore considered 

 simple, are really compound organs, and that 

 they are covered by other smaller papillae, 

 whose form and whose method of nervous 

 and vascular supply, show their true analogy 

 to the papilla of the skin. In physiological 

 exactness, and to carry out the analogy insti- 

 tuted by these anatomists, we may say that 

 these large papillae, so called, are no more true 

 papillae, than the long processes in the intes- 

 tine of the rhinoceros are true villi. Now, 

 these secondary, or true physiological papilla-, 

 are covered in by an even layer of epithelium, 

 in just the same way as the papillae of the 

 skin ; hence we see that the distinction gene- 

 rally laid down ceases. It would, however, 

 be too great an innovation to reject the name 

 of papillae for those organs that have so long 

 possessed it, and as the value and office of 

 their different parts will be implied in their 

 description, no misconception can arise. I 

 shall, therefore, continue the old nomen- 

 clature. 



There are three principal forms under 

 which the papillae, visible to the naked eye, 

 exist on the surface of the tongue. 1st. The 

 drcumvallate (caliciform, Cuv.), the largest and 

 fewest in number, and the most conspicuous, 

 situated at the junction of the middle and 

 posterior third of the tongue, where, by their 

 arrangement in two lines, having a direction 

 backwards and inwards, which meet in the 

 centre, they form a V-shaped ridge, with the 

 base directed forwards ; 2nd. The fungiform, 

 more numerous than the last mentioned, and 

 smaller, irregularly scattered over the centre, 

 sides, and apex of the tongue ; and, 3rd, The 

 conical or Ji/iform, by far the most numerous 

 and smallest, arranged in a dense pile over the 

 whole anterior two-thirds of the upper surface, 

 among which the last-mentioned are im- 

 planted. To these may be added a fourth 

 class of simple sessile papillae, first pointed out 

 by Professors Todd and Bowman as existing 

 on the apparently non-papillary surface im- 

 mediately behind the circumvallate papillae, 

 and which I have found also to exist on the 

 whole of the under surface of the free portion 

 of the tongue. 



The circumvallate papilla? are of the most 

 complex form, and may be considered as con- 

 sisting of two parts a central, button-like 

 projection, flattened or truncated at its free 

 surface, and a raised border surrounding it in 

 the form of a ring, of nearly equal elevation 

 with the central part, the two portions being 

 separated by a circumvallation, or fossa (b). 

 When a vertical section is made of one of 

 these papillae (_/?#. 754*.), the central portion is 

 seen to be in the form of an inverted cone, 

 and the surrounding fold is seen to constitute 

 a cup, at the bottom of which the apex of the 



Physiological Anatomy, vol. i. p. 435. 



