There are three principal forms under which the papillm, visible to the naked eye, exist on the surface of the tongue. 1st. The circumvallate (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 filiform, 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 papillm, first pointed out by Professors Todd and Bowman as existing on the apparently non-papillary surface im mediately behind the circumvallate and which I have found also to exist on the whole of the under surface of the free portion of the tongue.
The circumvallate papillm 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 papillm (fig. 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 cone is attached. At the attached portion the nerves and vessels enter, and the free trun cated surface, or base, of the cone is covered with small secondary papillm, concealed by the epithelium ( fig. 754. a); the free border is also surmounted by secondary papillm, so that it is, in fact, a circular compound papilla (c). The circumvallate papillm possess the utmost irregularity as to size, number, shape, and arrangement. Their number has been much overstated by some anatomists ; Cruveilhier gives it as from sixteen to twenty, Marjolin from nine to fifteen, Scemmering from twelve to fourteen, and illeckel from three to twenty. I think the number given by Messrs. Todd and Bowman, as from eight to ten, is much nearer the truth ; certainly, if ten can be counted, they must be considered well deve• loped ; frequently the number is below this — I have seen as few as five, or even four. In size they vary from that of an ordinary fungi form papilla to upwards of -th of an inch in diameter. They always assume more or less of the V-shaped arrangement, but the per fection with which the linear series is main tained, the straightness of the lines that form the angle, and the size of the angle so formed, all vary very much ; I have seen them stretch ing across from side to side of the tongue, almost in a straight line, with a third arm projecting back from the centre, something like the form of a tripod ; it is not uncommon to find a stray one or two scattered to a great distance beyond the prescribed line ; the cen tral one is frequently thrown hack half an inch, and sometimes a lateral one is found quite at the edge of the tongue. In shape, the varieties are chiefly owing to the relative size and development of the central tubercle and the circular ridge surrounding it. Sometimes one of these parts is suppressed, and then you either get what appears to be a large fungiform papilla, or a set of ridges having something of a circular or quadrilateral ar rangement, not to be distinguished from the fused rows of conical papillm which surround the circumvallate on all sides, and which are, in fact, continuations and prolongations of their calices. Haller mentions having seen the circumvallate papillm in two rows on each side ; I have met with a similar arrange ment on one side. This appearance may in some degree be accounted for by the supposi tion that the rows of conical papillm, among which the large fungiform immediately in front of the circumvallate are planted, have attained a circular or calyx-like arrangement around them ; for a large fungiform papillm, situated in a calyx so formed, would produce a very perfect papilla circumvallata. This change is just the reverse of that which reduces a cir cumvallate papilla to a fungiform by the sup pression of its surrounding ridge, and both, no doubt, are sources of irregularity. These papillm are supplied by branches from the glosso-pharyngeal nerve, which may be dis tinctly traced to them ; their vascular supply is abundant, and their epithelium thin and fine, so that during life, and when injected, they appear very red.
The fungiform papillm, as their name indi cates, have more or less of the form of a sphere supported on a pedicle ; this is their typical form, but they often deviate from it ; in size they vary from .Ath to nth of an inch.
They are scattered over the sides and tip of the tongue, and on the dorsum in front of the circumvallate. They may be dis tinguished from the filiform, among which they are implanted, by their red colour, in which, in the thinness and smooth ness of the epithelium investing them, and in the abundance of their vascular and nervous supply, they resemble those last de scribed. When examined microscopically, they are seen to be covered on their sides and summit with secondary papillm (fig. 755.A), to which, in injected specimens, the individual loops of capillaries may be seen projecting with great regularity and beauty (B). The fungiform papillm are largest about the centre of the tongue, smallest along the edges, and most numerous at the sides of the tip, but they are liable to the greatest variety in their size and distribution ; I have seen them so large about the centre of the tongue, as almost to equal in size the circumvallate ; I have seen them so numerous at the tip, as nearly to equal in number the filiform among which they were scattered ; again, in the same region, I have seen them so scanty, that they could hardly be said to exist there.* The conical or fitiform papillm, the third class, constitute the great mass of the papillary structure; they cover, in a close-set pile, the whole of the anterior two-thirds of the tongue, being limited behind by the circum vallate, and having the fungiform scattered among them : it is their structure that imparts the rough coriaceous character to the papil lary surface, and they constitute the fur in the centre. They are altogether smaller, but in length they exceed, at least in the centre, the other two forms, and they exhibit greater di versity of structure and a more complete ab sence of typical shape than either of the other varieties. They affect in some situations a linear arrangement, principally at their con fines, that is, in front of and around the caliciform papillm, where they are continuous with the elevations that surround these pa of which they are the continuations forwards and outwards, and along the whole free margin of the tongue, except at the tip, where the linear arrangement cannot be traced. In the first-mentioned situation their rows run forwards and outwards, coinciding with the arms of the V-shaped figure that the cir cumvallate papillm assume ; in the last-men tioned, they are placed vertically along the sides (fig. 745. i i): they have been well de scribed and figured by Scemmering.* Along the centre of the tongue, in the neighbourhood of the median furrow, the conical papillm often assume a cracked and fissured appearance ; but the linear arrangement is less marked here, and the fissures have no determinate direc tion, but can be made and effaced according to the movements of the tongue. The conical papillm are largest in the neighbourhood of the circumvallate, where they are truncated, and where some of them assume almost a fungiform shape : they are longest about the centre of the tongue, near the median line, and smallest in the anterior part, near the side and tip. The form of the projections of base ment membrane, on which the epithelium is placed, constituting the mould of the true papillary structure, is generally something of a cylindrical shape, the top supporting second ary papillm, or it is conical, the secondary papillm being continued more or less down the sides : or the base is small, and supports a more expanded portion, and thus the conical is seen to pass into the fungiform shape. But it is in the epithelium that the characteristic 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 papillm under its smooth invest ment, the scales being arranged parallel to the surface ; but in the conical and filiform papillm 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 papilke. Where the secondary papillm 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 maim from which they spring are true hair papillae, 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 fig. 758. ; indeed in c the chief difference is in the direction of the imbrication : in some morbid specimens I have seen it even closer.