OCR Text |
Show 396 MR. W. P. PYCRAFT ON THE [Mar. 21, borders are straight, its posterior border is V-shaped. It does not extend forward beyond the level of the anterior ^ of the vertically elongated squamosal. Its outer posterior border runs from the angle of the lower j of the squamosal (Pl. XXIII. fig. 1) inwards to the upper half of the lateral border of the supraoccipital ; its inner posterior border is in part approximated to but not yet fused Avith the supraoccipital, and in part free, bounding, with its fellow of the opposite side, the parieto-occipital fontanelle, as the supraoccipital bounds it ventraily. The frontal is broadest posteriorly. Its mesial and posterior borders are straight. The latter, skirting the parietal posteriorly, sweeps forAA-ards to the inner side of the squamosal, to articulate with the alisphenoid (Pl. XXIII. fig. 1). The free outer border is grooved for the supraorbital gland. The region aboAre the alisphenoid constitutes the orbital plate of the frontal and is of small extent. The squamosal is crescentic in form, the concave border forwards. The tip of the upper limb is free and bounds the supraorbital grooA*e posteriorly, furnishing the squamosal spines, so conspicuous in the species from which this description is taken, Pelecanoides and Cymodroma. The lower limb furnishes the squamosal prominence. It is almost entirely excluded from the inner wall of the skull. The nasal is of great size, and conspicuously convex dorsally. It forms the outer roof of the large olfactory cavity. Beneath it lies the horizontal plate of the mesethmoid. Its posterior end is embraced on either side by the frontal. It is deeply notched forwards to form the anterior and external nasal processes. These constitute the posterior boundary of the narial aperture, which is holorhinal. The lachrymal does not differ from that of the adult, p. 387. The premaxilla has fused completely with the maxilla, even in the youngest of the two skulls. The nasal process yet, however, remains distinct. The jugal and quadrato-jugal can only be imperfectly distinguished one from another and from the maxilla, Avhich differs in no important particular from that of the adult. The relations between the vomer, palatines, and pterygoid recall those betAveen these elements in Rhea (Pl. XXIII. figs. 3, 4). The vomer consists of a pair of elongated, flattened larainas united in the median line anteriorly. The free posterior ends are received by the concave anterior borders of the hemipterygoids, and are bounded, on either side, by an inwardly turned scroll of bone from the dorsal border of the palatine. The palatine is stiil free, its anterior end is traceable nearly as far forwards as the tip of the jaw. Posteriorly it develops a strong dorsal keel Avhich eventually turns inAvards and forwards to embrace the posterior lateral border of the vomer. The pterygoid is rod-shaped, and continued forwards to articulate with the vomer by means of a large hemipterygoid |