| OCR Text |
Show 30 DR. J. MURIE AND MR. A. D. BARTLETT [Jan. 9, cutting-edges of the outer and inner sides of the lower incisors, and justly attributed to the closing of the lower upon the upper jaw with the separation of the lower incisors the effect of producing closer contact between the cutting-edges of both jaws upon one another, yet he has failed to notice the use, and mode of application of the inner cutting-edges of the lower incisors. Professor Owen, in his valuable memoir " on the Osteology of the Marsupialia," in the 'Transactions of the Zoological Society,' 1841, vol. ii. p. 394, does not mention anything from which it would be inferred that the lower incisors are used in the manner we have described ; he says, however, among other things, that, excepting the Koala, " in all the other marsupial crania which I have examined, the rami of the lower jaw are not anchylosed at the symphysis." Having satisfied ourselves of the occurrence of the mobility of the teeth and symphysis of the lower jaws in the living animals, it became an object of interest to ascertain in the dead ones how this was produced ; and for this purpose we commenced by studying the bones in a few macerated skulls. In one of these, an adult specimen of Macropus major (M. gigan-teus), the two halves of the inferior maxilla of which have been completely separated, when the symphyses are applied closely together the two lower incisors are approximated at their anterior half or points upon the inner edges; while the posterior halves of the incisors have an interval of nearly one-eighth of an inch, of a somewhat spear-shape. The two margins of the incisors in apposition are worn and flattened, evidently by the continued attrition of the one upon the other. The symphysis of the bones at the part where they are most closely applied is at the posterior half; and there they unite, though loosely, by an articulation in the manner of a diaphysis. In a Macropus ocydromus the symphysis and teeth of the mandible exhibit very nearly the same appearances. The same parts in Osphranter antilopinus differ in the anterior and inner cutting-edges of the incisors not coming together so sharply, by reason of the points being more rounded and set outwards than in the two former species. When the teeth are separated there is an open space of fully one-eighth of an inch ; there is also a diminutive ovate space at their base, which may in part be a natural deficiency; but likewise the dental tissue seems partially abraded as if worn by the action spoken of, possibly by the tearing of grasses or other, harder stems. The shape and position of the incisors of Halmaturus agilis approach those of Macropus major; the interval at the base of the teeth, however, is relatively wider and correspondingly shorter than in that larger species. Halmaturus irrna presents no remarkable difference from Macropus major, excepting in the mandible being less in dimensions, and consequently having a smaller separation of the teeth. Besides an examination of the dried bones, we have been fortunate in having the opportunity of studying the appearances in two animals which have recently died in the Gardens. In one of these, Bennett's |
