| OCR Text |
Show 1883.] TONGUES OF THE MARSUPIALS. 625 upon an oval area surrounded by gland-ducts. Owing to the delicacy oi these terminal organs the area became protected by a fold round its circumference in which all the bulbs except those of the central line were sheltered. This is the stage represented in the figure and has not proceeded further because the whole structure is additionally protected by its position in the tongue, t. b. taste-bulbs. /. h. p bme hur-hke papilla; covering the posterior part of the organ ' j ••fj.» hail'-llke papilla? posterior to the bulb-bearing organ and of different form from the others, gld. d. Gland-duct of serous gland. Fig. XIII. x 14-5. Transverse section of the obliquely directed anterior bulb-bearmg ridge of Ornithorhynchus. gld. d. Duct of serous gland opening into the narrow space between the ridge and the cavity in which it is placed. The ridge is placed upon a very exposed part of the tongue, and is therefore most exceptionally protected, beinc only reached from the surface through a narrow chink (probably clo°sed by a sphincter muscle). The necessity for this extreme protection is probably to be found in the structure of the bulbs, which is very different from that of higher mammals. Fig. xiv. X 14-5. Vertical longitudinal section through the left anterior circumvallate papilla of Halmaturus ualabatus. c. p. Coronate papilla. The taste-bulbs (t. b.) are now of the normal marsupial type (leading up to those of the higher mammals, but showing traces of development from the cells of an interpapillary process), and are probably less sensitive than those of Ornithorhynchus, which are essentially subepithelial. The apex of the papilla emerges from the cavity in which most of it is placed, but the part thus exposed is not covered by taste-bulbs, which are present over all the protected part (nearly the whole). The apex is directed forwards and the symmetry is bilateral. It is very likely that the mouth of the depression can be closed. Fig. xv. X 1 4 5 . A^ertical section through one of the anterior circumvallate papilla? of Belideus breviceps. The apex is directed inwards rather than forwards, but the two papillae are bilaterally symmetrical together, if not so individually. Fig. xvi. X14-5. Vertical longitudinal section through one of the anterior circumvallate papilla? of Phalangista vulpina. The apex is directed forwards, gld. Gland of which the ducts (gld. d.) are seen opening into the space between the papilla and its cavity. Fig. XVII. X 14-5. Vertical section through the posterior circumvallate papilla of Belideus breviceps. It is likely that this papilla is radially symmetrical, for the difference between the two sides is probably accidental. The overhanging surface which bears the bulbs is a trace of the structure shown in the preceding figures. Otherwise the shape resembles that of the higher mammals. It is very interesting that the anterior and posterior papilla? of the same tongue should belong to such different types (figs. xv. & xvn.). Fig. XVIII. x 145. Vertical section through a circumvallate papilla of Perameles nasuta. Very similar to the last, but symmetry decidedly radial. All the three papillae in this species are of the same type. Fig. xix. x40. Horizontal section through the depression (c. v. p. o.) leading into the cavity containing the posterior circumvallate papilla of Halmaturus ualabatus. The opening is surrounded by an irregular ring of fine papillae (r. f. p.) (not aggregated into coronate papillae). This section indicates the extreme narrowness of the opening into the cavity. It is very probable that the mouth can be closed by a sphincter, and that it is contracted in this instance. Fig. xx. x40. Vertical section through the posterior circumvallate papilla of Phalangista vulpina. This papilla also belongs to the higher type, while the anterior papilla of the same tongue is shown in fig. xvi. Most of the references have been previously explained, gn. c. Ganglion- cells arranged in groups at the lower part of a mass of nervous |
