OCR Text |
Show 1883.] TONGUES OF THE MARSUPIALS. 619 continued into two horns which pass anteriorly round the papilla outside the ring of secondary hair-like papilla?. As the section is taken at successively higher levels, these horns are prolonged further and further anteriorly until they seem to meet and enclose the whole papilla. (Thus fig. XXIII. Plate LV. represents a section taken rather low.) The cornified cells of the hooks are remarkably hard, so that the razor cuts them with a very audible sound and with much detriment to its edge; they remain bright yellow after treatment with logwood. A vertical longitudinal section through one of these papilla? is drawn in fig. XXII. Plate LV., and it shows the great size and strength and the curvature of the posterior hook; it also shows the thin anterior corneous layer first appearing where the hook becomes clear of the main papilla. Both these figures alluded to are semi-diagrammatic, and are in some points the probable interpretation of very doubtful appearances due to changes in the tissues. This region is very interesting, for it shows how the slender elements of the coronate papilla? have been modified to perform the tough work of the horny filiform papillae of higher animals. It is obvious that the strong posterior hooks would first meet any object, and would be obliged to do practically all the work, when the tongue was drawn backwards in licking. The coronate papilla? above the tip, in front of this peculiar region, are of more regular form; but the posterior secondary papilla (and occasionally one beside it) is more strongly cornified and larger than the others. The cornification also tends to pass anteriorly round the outside of the other secondary papilla? as two horns. In these points there is a transition towards the modified papilla? described above, but the characters increase very suddenly at the limits (posteriorly also) of the peculiar region. The secondary papilla? in the rings are not numerous, 6-8 being common; they are much recurved : the papilla? are small and numerous, i. e. about 72 to the square millimetre. There are no isolated hair-like papillae. The coronate papilla? just in front of the anterior circumvallate papillae are rather small and closely packed (about 60 to the square millimetre) ; they are round or oval, and some irregular in shape. A few are remarkably elongated antero-posteriorly (see fig. xxiv. Plate LV., in which the effect may be increased by a slight obliquity of section, but is remarkable anyhow) : such elongated papilla? are doubtless formed by longitudinal coalescence, as I have seen traces of a central constriction, and the number of secondary papilla? is about twice the usual number (8-10). There is no special size or cornification in the posterior secondary papilla?. Isolated hair-like papilla? are not present. The upper cells of the papilla? stain deeply, as has been described in Perameles; in fact these posterior coronate papilla? are very similar to those of Perameles. They are recurved, but less than the anterior papilla? ; they are not of the tall slender type like the posterior coronate papilla? of Belideus, but are more like the posterior type of Perameles, differing from these in the o-reater symmetry of the ring of secondary papilla? when cut horizontally. The modified papilla? described above are transitional |