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Show 1901.] REPTILES F R O M PATAGONIA. 171 Its peculiar contour is evidently due to the fusion of large dermal ossicles with the bones of the cranial roof and cheeks; but all the sutures are obliterated, except on part of the palate. The hinder third of the skull, as seen from above (Plate X V . ), is merely an occipital crest (occ.) consisting of two anteroposterior!^ compressed, almost laminar bosses of bone, which meet for half their depth in the middle line and fuse together. This crest seems to be solid and is firmly anchylosed with the occipital border of the skull, from which it inclines both upwards and backwards. It is attenuated to a sharp edge at its upper and lateral margins, which seem to be complete on the right side of the fossil; audits upper margin shows a rounded median excavation at the meeting of the two elements of which it is composed. O n either side an extremely thin lamina of bone connects the basal half of the occipital crest with a bovine-horn-shaped boss (i.) which projects laterally from the cranium just above the hinder part of the quadrate bone. This postero-lateral prominence is well-preserved on each side of the fossil, and its extent equals that of the crest just described. It is triangular in section, its antero-superior face being largest and flattened ; and it exhibits a slight curvature which causes its acute distal extremity to point both backwards and outwards. Immediately in front of the occipital crest there are three bosses completely extending from side to side of the cranial roof. Of these the median or interparietal one (II.) is the smaller and ovate in shape, with its long axis antero-posteriorly directed, and its upper face concave in the middle. Of the lateral (or parietal) pair (in.) only that on the right side is complete. It is trapezoidal in shape, about as broad as long, and gently rises into a slight, blunt prominence near its middle. It extends nearly as far forwards as the orbit (orb.), above which the cranial roof is also thickened. This thickening is separated by a constriction both from the nasal region, which is flattened, aud from a small median triangular area in the frontal region, which is occupied by three low bosses-a pair (iv.) behind, a median one (T.) in front, all broader than long. At the base of the postero-lateral horn-shaped prominence on each side there is also a well-preserved, small, laterally-directed boss (vi.), which is depressed and is about on the same level as the roof of the orbit. All the bosses just described are also visible in a side view of the skull (Plate XVII.), which exhibits a still smaller, antero-posteriorly elongated, rounded boss (TH.) on the cheek immediately in front of the auditory opening. As shown on both sides of the fossil, there is no excavation of the cheek-plates between the orbit and the auditory opening, but the line of the alveolar border is continued directly backwards to the quadrate bone. The nasal roof does not extend farther forwards than the premaxillae, but the lateral margin of the terminal narial opening (na.) is excavated by a constriction between the nasal and maxillary bones. This constriction is continued as a groove to the anterior margin |