OCR Text |
Show 1899.J FROM THE LONDON CLAY OF SHEPPEY. 779 Immediately in front of the rostral hinge the upper surface of the beak is broad and slightly convex from side to side ; but as it passes forward between the nares (n.) it becomes narrower and more rounded, and continues to do so as far forward as preserved, the tip being lost: between the nostrils a portion of the bone is broken away showing that it is hollow. The nostrils (n.) are very long and narrow, and extend backward nearly to the rostral hinge. They are widest immediately in front of the antorbital fossa, and thence run forward as a narrow cleft, which anteriorly probably becomes a groove (n.g.); the anterior end of the narial opening (or groove) is broken away with the tip of the beak. Posteriorly the nostrils are separated from the antorbital fossa by a bar of bone which no doubt is, as usual, formed by the union of the downward process of the na^al with the maxilla. The edge of the beak is formed by a bar of hone, which is narrow anteriorly but widens out gradually from before backward, reaching its greatest width just in front of the antorbital fossa. Behind this it passes without interruption into the quadrato-jugal bar (jug.). The thickness of this bar seems to be constant throughout its length, but the posterior extremity where it joined the quadrate has been broken away. The interorbital septum (i.o.s.) is incomplete, being perforated by a large quadrate fenestra (i.o.f.), similar to that seen iu Phaethon. It has been cleared of matrix so that the thickened ventral edge (rostrum) is exposed, and it can be seen that the anterior ends of the pterygoids rest against it and articulate with the posterior ends of the palatines as in most Cari-nate birds. Unfortunately, it has not been possible to work out the structure of the palate further. The quadrate (q.) is long and articulates with the skull by two heads, the facets for which are situated very far back, immediately within the rim formed by the lower edge of the paroccipital. On the exposed side the outer half of the quadrate has been abraded, and its distal articulation is still in its natural position with regard to the mandible, so that its form cannot be observed. Rather high up on the inner border of tbe bone there arises a fairlv large orbital process (o.p.) which projects upward and inward and terminates in a blunt point. In the mandible the posterior end is so much injured that its form cannot be determined, but there seems to have been a fairly prominent postero-internal process. From its posterior end the ramus increases in depth as far forward as about the middle of the orbit. At this point there is a lateral vacuity which is continued forward as a shallow depression, most clearly defined above, and of which the anterior end is opposite the middle of the nostril. In front of this depression the mandible tapers towards its anterior end, and its outer surface becomes rounded from above downward ; the extreme tip has been broken away. It cannot be seen whether there was a distinct coronoid process or not, because the upper border is hidden behind the jugal bar. Beneath and behind the lateral vacuity the suture between the dentary and the articular region remains distinct. |