OCR Text |
Show 202 MR. E. T. NEWTON ON SOME [^Pr- 2> which is also in relation with the supraoccipital (s.o.) and with much smaller bone (pt.ot.) which lies behind it. This plate (sp.ot.) has on its under surface a deep depression, which evidently formed the attachment for the hyomandibular; the depression is not, however, quite confined to this plate, but seems to extend for a short distance on to the smaller bone which lies behind it. These two bones, therefore, which have combined to support the hyomandibular, are regarded as the sphenotic (postfrontal) and the pterotic (squamosal). The last-named bone comes into relation with the supraoccipital on the inner side and has behind it two elements, the outer of which is evidently the post-temporal (pt.tem.) and the inner one (pu.) is either the parietal or epiotic. Another bone which is found behind these in the recent Arius has evidently been lost in this fossil. The post-temporal (jit.tem.) has a peculiar and characteristic structure. On the upper surface of the skull it presents a flattened tuberculated plate, which, a comparison with the recent Arius gagorides shows, is composed of two parts-an anterior, united with the pterotic, and a hinder one attached to the hone directly on its inner side, the parietal (or epiotic), and extending as far as the supraoccipital. The post-temporal must also have been in close relation with the bone behind it, which has been lost; but the smooth surface now exposed does not indicate a close attachment. The outer extremity of the post-temporal has a very distinct socket for the upper part of the supraclavicular, and from below this a strong bar of bone passes downwards and inwards quite to the base of the skull, to which it has been firmly attached. There is a thin plate of bone (x) behind this bar, which seems to have been separated from it by the crushing of the skull, that passes backwards and inwards, seemingly to join the broad thin horizontal plate formed by the transverse processes of the vertebrae ; indeed, it may be that this is a part of the transverse process, extending forward to join the post-temporal. The hinder part of the supraoccipital is wanting, but the front part is preserved and is somewhat shield-shaped, having its margins on each side indented by a series of curves where it is united with the frontal, sphenotic, pterotic, and parietal. The hindermost temporal plate, now wanting, was doubtless also in contact with the supraoccipital. The base of the skull is much crushed, but it seems quite certain that the brain-cavity was completely enclosed by bony walls. The buttress-like supports of the post-temporal bones are striking features of this region. Just in front of the left buttress may be seen the remains of an inflated bulla, which lodged one of the large otoliths, and still further forward there is on each side a depression for the attachment of the hyomandibular (hm.). In front of this again is another pair of elongated depressions, evidently the ethmoid attachments for the prefrontals (fig. 2, eth.). The most anterior part of the baee, in its present condition, is formed by a fan-shaped mass, which is apparently in part the vomer and in part the ethmoid. Three or four of the anterior vertebrae are firmly united to each |