| OCR Text |
Show 298 ON THE SKULL OE ORYCTEROPUS GAUDRYI. [Feb. 18, position of the condyle, which is borne upon a much shorter pedicle and has a more horizontal articular surface. The minute structure of the teeth is precisely as in 0. capensis, so that they give no indications of the possible origin of their peculiar character. In the left maxilla six teeth remain in place, and in front of them is an empty alveolus ; on the right there are five teeth and two alveoli. The most anterior tooth preserved is pm. 3 (counting from behind forward); this is small and laterally compressed, its flat crown slopes downward and forward. The next is similar, but less compressed. The hindermost premolar is a stout simple tooth; its worn crown consists of two flat surfaces meeting in an angle and forming a transverse ridge. The two first molars are very similar to those of the recent species, but the last (m.3) is rather different. In the living forms it is somewhat variable in shape, but usually consists of a single column and is nearly circular in section; in one skull from Somaliland, it is, however, oval in section and shows traces, at least on the outer side, of division into two lobes, the hinder being much the smaller. The circular type of tooth evidently results from the reduction of the hinder lobe, which in the fossil is only a little smaller than the anterior one, from which it is separated by a well-marked vertical groove on the outer side and a less distinct one on the inner. In a young skull of a recent species, in which the last molars are only just coming into use, they are distinctly bilobed, so that the upper part of the crown of the unworn tooth resembles in form the worn molar of the Pliocene species. In the mandible six teeth are preserved on both sides. The two anterior ones are much compressed; the next is stouter and its grinding surfaces form a transverse ridge. The first two molars are similar to those of the living species : the third (m.3) is clearly bilobed and is nearly as long as m.2. In the recent species the division into columns is distinct only on the inner side, and the tooth is much shorter from before backward than the preceding one. The dimensions of the skull and mandible are:- Skull. Width between ends of postorbital processes.. 53 millim. Outside width at postglenoid processes 60 „ "Width of cranium behind postorbital processes 36 „ Greatest width of occipital surface 52 „ Height of foramen magnum 13 Width „ „ 22 „ Distance between postorbital process and zygoma 17 „ Mandible. Height at coronoid process 65 millim. „ „ condyle 52 „ Height of ramus behind last molar 16 „ „ „ in front of first molar 12 „ |
