OCR Text |
Show 152 DR. F. P. MORENO AND MR. A. S. WOODWARD ON [Feb. 21, Scleropleura bruneti^, the bony plates and tubercles are still covered only by epidermis, although most of them are reduced to small nodules and might well have sunk more deeply into the abnormally hairy skin. There is also reason to believe that in the gigantic extinct Armadillos of the family Glyptodontidse the same arrangement of dermal structures prevailed; for one specimen of Panochthus tuberculatus obtained by Dr. Moreno for the La Plata Museum actually shows the dried horny epidermis in direct contact with the underlying bone, and seems to prove that the numerous perforations in the Glyptodont dermal armour Avere not for the implantation of hairs (as once supposed), but for the passage of blood-vessels to the base of the epidermal layer. Similarly, among the extinct Ground-Sloths of the family Mylo-dontidse dermal ossicles have been found with the remains of Ccelodon2 and various forms (perhaps different subgenera) of Mylodon; but the only examples of this armour yet definitely described 3 exhibit a conspicuously sculptured outer flattened face, and it thus seems clear that Burmeister was correct in describing them as originally reaching the upper surface of the dermis and only covered externally by a thickened epidermis. Three such dermal tubercles, now in the British Museum, are shown of the natural size in PI. X V . figs. 4-6. It is, hoAvever, to be noted that Burmeister himself actually observed armour of this kind covering only the lumbar region of the trunk. He believed that the other parts of the animal were similarly armoured, because he had found " the same ossicles " on the digits of the manus, Avhere they Avere "generally smaller and more spherical"; but he unfortunately omits to make any explicit statement as to the presence or absence of the characteristic external ornamentation on the latter. The omission just mentioned is especially unfortunate because on careful comparison it is evident that the irregular disposition of the small ossicles in the piece of skin now under consideration is most closely paralleled in the dermal armour of the extinct Mylodon, as already observed by Drs. Moreno and Ameghino. There is obviously no approach in this specimen to the definite and symmetrical arrangement of the armour such as is exhibited both by the existing Armadillos and the extinct Glyptodonts. There are, then, two possibilities. Either the dermal armour of Mylodon varied in different parts of the body, being sculptured and covered only by epidermis in the lumbar region, while less developed, not sculptured but completely buried in the dermis in the comparatively flexible neck and shoulder region-in which case Dr. Moreno may be correct in referring the problematical specimen to Mylodon; or the dermal ossicles of 1 A. Milne-Edwards, " Note sur une nouvelle Espece de Tatou a cuirasse incomplete {Scleropleura bruneti)," Nouv. Arch. Mus. vol. vii. (1871) pp 177- 179, pi. xii. 2 P. W . Lund, K. Dausk. Vidensk. Selsk. Afkandl. vol. viii. (1841), p. 85 (footnote). 3 H. Burmeister, Anales Mus. Puhlioo Buenos Aires, vol. i. (1864-69), p. 173, . pi. v. fig. 8. |