. On the Fossil Mammals of Australia. Part III. Diprotodon australis, Owen . and continuation of enamel to the widely openbase of the tooth. I have no evidence that the first and smallest of the series of fivegrinders in Phascolomys is a premolar or replacing tooth, and view it, therefore, as oneof the first developed calcified series. It is analogous, in function, in retention, andlong-continued use, to a premolar of the placental type-dentition. The succeeding fourgrinders in both Phascolomys and JDiprotodon are equally members of the first set ofteeth; and the last three are homologous with
. On the Fossil Mammals of Australia. Part III. Diprotodon australis, Owen . and continuation of enamel to the widely openbase of the tooth. I have no evidence that the first and smallest of the series of fivegrinders in Phascolomys is a premolar or replacing tooth, and view it, therefore, as oneof the first developed calcified series. It is analogous, in function, in retention, andlong-continued use, to a premolar of the placental type-dentition. The succeeding fourgrinders in both Phascolomys and JDiprotodon are equally members of the first set ofteeth; and the last three are homologous with those that are not displaced by verticalsuccessors in diphyodont Placentalia. The symbols, therefore, dl 3, d^ 4, m 1, m 2, m 3,express, in my opinion, the homologies of the f nnctional molar teeth of Biprotodon withthose, ^ so marked in Hyraw^ Hippopotamus^ and Sms^. For convenience of com-prehension of the teeth symbolized in Plates I subjoin woodcuts ofan instructive phase of dentition in the Hog (fig. 3) and Kangaroo (fig. 4), \ ^^y V Figs. 3 & § 5. Spinal Column,—Of the atlas there is a portion of the left moiety (Plate 2) showing the deep articular cavity for the occipital condyle of the same side,between which and the diapophysis is the outlet of a canal {a) about 3 lines in diameter,which traverses the neural arch from within outward behind the upper part of the cavityfor the condyle. The surface {z^) for the articular process of the axis is slightly concave;between its upper part and the ridge leading from the hind margin of the neural arch tothat of the diapophysis there is a deep and wide groove for the passage of the vertebralartery into the neural canal. The above-described fragment yields evidence that, as inMacropus, Phascolomys, Phascolarctos, and some other Marsupials, the ring of the atlas(if indeed it were completed below by bone in Biprotodon) presented only the perforation * In my < Anatomy of Vertebrates/ vol. ii. p. 4
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