TONGUE 



1139 



is to be found. In the other forms we saw it 

 continued over the whole compound organ as 

 a thin indusium, covering in and concealing 

 the secondary papillae under its smooth invest- 

 ment, the scales being arranged parallel to 

 the surface; but in the conical and filiform 

 papillas we not only see the epithelium exist- 

 ing in much greater quantity, but over each 

 secondary papilla assuming a vertical arrange- 

 ment, and, after continuing compact for some 

 little distance, breaking up into a brush of 

 hair-like processes (fig. 756.), the number 

 coinciding with that of the secondary papillae 

 Where the secondary papillas are few the hairs 

 are few, where they are many the hairs are 

 many, and each hair may be traced down, by 

 following the line in which the epithelium is 

 vertical, to each papilla. In fact, these pro- 

 cesses are true hairs, and only differ from other 

 hairs in being short, uncompact, imperfectly 

 elaborated, and in having the imbrication 

 retroverse instead of directed forwards ; and 

 the secondary papillae from which they spring 

 are true hair papillee, differing only from ordi- 

 nary hair papillae in being raised and grouped 

 on a common pedicle instead of sunk in a 

 proper follicle. In some cases the resemblance 

 of these filaments to ordinary hair is very 

 close indeed, as seen in Jig. 758, ; indeed in c 



Fig. 758. 



Hair-like processes of filiform papilla, 

 a, Mag. 150, b and c, 100 diameters. 



the chief difference is in the direction of the 

 imbrication : in some morbid specimens I have 

 seen it even closer. 



Now this difference in the arrangement of 

 the epithelium on the different papillae in- 

 dicates, I think, a very important physiolo- 

 gical distinction ; in one case we see the sen- 

 tient papilla? covered by a thin layer of a fine 

 epithelium, thinner over them than in the in- 



tervals between them ; in the other case we 



see each secondary papilla the seat of a rapid 

 generation of epithelium that clothes the 

 whole compound organ with a dense impene- 

 trable brush of hairs 



this latter arrangement 



seems as inconsistent with the possession of 

 sensibility as the former seems adapted to it, 

 and the difference would suggest to me the 

 division of the papillae into "sentient" and 

 "protective ;" among the former I would class 

 the circumvallate and the fungiform, among 

 the latter the filiform and, with a certain qua- 

 lification, the conical : but I shall return to 

 this presently in speaking of the functions of 

 these papillas. The great difference between 

 the filiform and conical forms is in the amount 

 of the epithelium : in the filiform it is such 

 as has just been described j in the conical, the 

 hairs are very short and thick, and terminate 

 in an even plane almost as soon as they be- 

 come separate, so that they have not at all 

 a filamentary character. This epithelium is 

 being constantly generated and as constantly 

 thrown off, as is shown by the variation in the 

 quantity of fur on the tongue from day to day. 

 It is in these papillae that the separation into 

 two layers is best seen (Jig. 757. <?/), and the 

 appearances of this separation are such as to 

 make me think that the method of desqua- 

 mation is not by the shedding of individual 

 scales, but by the throwing off of the upper 

 layer, the under layer taking its place, itself 

 to become divided into a deep-seated and su- 

 perficial portion, and to be in turn thrown off 

 as it grows older. The vascular supply of these 

 papillae is very abundant, as might be expected 

 from the rapid nutrition that is taking place 

 from their surface. The pigmentary character 

 of the epithelium, at least under some circum- 

 stances, has been already referred to. 



The simple papillas are scattered beneath 

 the apparently non-papillary surface behind 

 the circumvallate, beneath the edges of the 

 tongue, and on the under surface of its free 

 portion, also among the conical and filiform ; 

 in the former situation they resemble the 

 secondary papillae of the circumvallate and 

 fungiform, in the epithelium being continued 

 smoothly over them ; in the latter, those of 

 the filiform, each being the base of a hair- 

 like process. The situation of these pa- 

 pillas, their number and arrangement, is very 

 well shown by injection, when the individual 

 loops of capillaries may be seen passing up 

 from the sub-mucous plexus at regular inter- 

 vals, one to each papilla. The method in 

 which the conical papillae of the upper sur- 

 face pass into the simple of the under, is this : 

 the ridges on the side of the tongue, to 

 which reference has already been made, con- 

 sist of fused conical papillae arranged in linear 

 series vertical to the edge, and, like them, 

 crowned with secondary papillae ; as they pass 

 down the edge towards the under surface they 

 become shallower, so that by the time they 

 have reached that surface, the secondary pa- 

 pillas, instead of being elevated, are sessile, 

 and immediately subtended by the cutis. This 

 is the true nature of those vertical ridges on 

 the edge of the tongue described by Bichat, 

 Scemmering, and many other anatomists. 



Structure of papillae. The nature of the 

 true papillary structure, i. e. the contents of 

 the projection of basement membrane, seems 



4 i) 2 



