| OCR Text |
Show 1892.] FROM THE OLIGOCENE OF ITALY. 79 external wall, the anterior root of the zygomatic arch, a portion of the floor of the orbit, and the aperture of the canal for the fifth nerve. At the hinder extremity of the palatal surface are preserved two molariform teeth, which are almost or quite untouched by wear, and are, fortunately, uninjured. By filing away the alveolar parapet in front of the anterior one of these teeth, there have been revealed the two roots of a third tooth. Behind the last remaining tooth there is a portion of the alveolus of a fourth tooth which had evidently not been protruded from the gum. Now "the unworn condition of the two remaining teeth and their Figs. 1, la, 1 b.-The third and fourth left upper milk-molars of a young individual of Prorastoma veronense, viewed from the oral and outer aspects; 1 a is f, the others \. pr„ protocone; pa., paracone ; me., metacone; hy., hypocone. The letters a, b, c, d, indicate the parts of the hinder tooth which correspond with those similarly lettered in fig. 2. Fig. 2.-The third left upper molar of Merycopotamus dissimilis. Letters as in preceding figure. \. position with regard to the anterior root of the zygomatic arch, coupled with the alveolus of the unprotruded fourth tooth, clearly indicate that the jaw belonged to an exceedingly young animal. And, apart from their structure, we should further be justified in regarding the two entire teeth as belonging to the deciduous series if their owner were a diphyodont mammal, or to the premolar series if the animal were monophyodont. There are, however, considerations which enable us to determine the serial homology of the teeth more definitely. Each of the two teeth carries on its crown well-marked but discontinuous transverse ridges, separated by deep valleys. In the hinder tooth the crown is oblong and nearly symmetrical, and carries |
