82 EDWARD B. POULTON. 



anil backwards instead of backwards merely, and the superior 

 and posterior side of the ring is chiefly developed. 



Within the ring the summit of the main papilla is concave, 

 the greatest depth being attained near the anterior part of the 

 ring (or inferior and anterior side in the case of the lateral 

 papillae). This is because a far longer incline of central cells 

 leads up to the posterior hair-like processes than to the ante- 

 rior (see fig. 11, &c.), and this difference is especially marked 

 in the posterior part of the tongue, while it almost disappears 

 in front (fig. 4). Transverse vertical sections show that the 

 rings are developed equally on both sides of the antero-pos- 

 terior diameter, but as the hair-like papillae bend sharply back- 

 wards they are only cut through near their bases (fig. 5). The 

 same bilateral structure is seen in horizontal sections (figs. 6 

 and 12). Each papilla is seated upon a single main papillary 

 upgrowth from the mucous membrane. 



The relation of this to the secondary papillae is best studied 

 in horizontal sections at various depths (figs. 6, 7, and 12). In 

 such sections the papillary process is almost circular in section 

 at the lowest level, but a very little higher there is an inter- 

 ruption at one point of the margin by a small ingrowth of cells, 

 which a little higher becomes so large as to convert the ori- 

 ginal simple involution into a ring, incomplete only where the 

 central mass of cells is continuous with the epithelium outside 

 the ring. These appearances are due to the primary papillary 

 involution growing upwards as a ring everywhere except ante- 

 riorly, and therefore the first appearance of the ingrowth of 

 cells indicates that this is the anterior part of the margin. 

 The mass of cells within the ring is convex below, and at the 

 same time slopes slightly downwards anteriorly, and is con- 

 tinuous with the wall of the ingrowth (see fig. 4, A end). 

 Therefore, this point is first reached in horizontal sections from 

 below upwards. The extension of the primary process into 

 the ring is well seen in transverse vertical sections (fig. 5), 

 and less well in longitudinal vertical sections, for here the 

 section passes through the incomplete point of the ring or near 

 it, where the ring is less developed. 



