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Show 38 MR. W. P. PYCRAFT ON THE [May 2, broad limbo indistinguishably welded with the palatines, agreeing in this with Calyptomena and Cymbirhynchus. The palatine (PI. II. fig. 2 a) in Calyptomena is a long bone: anteriorly rod-shaped, it extends backwards as far as tlie under surface of the antorbital plate, when, after sending outwards a prominent, rounded elbow- " transverse bone it turns abruptly inwards, ultimately forming a roughly spatulate plate, bent upon itself so as to form a long linear surface running along the parasphenoid rostrum, and fusing mesiad with the vomer and a free downwardly hanging curtain to form a cavernous space in the roof of which is the base of the vomer. The palatine of Chasmorhynchus differs from that of Calyptomena in the greater width of the hinder laminated portion and the more extensive development of the inferior free edge, forming the cavernous space beneath the vomer. This edge now appears rather as a shelf-like projection developed from the inner border of the shaft of the palatine. In Cymbirhynchus the palatine shaft is broader than in Calyptomena, and this increased breadth is especially noticeable at its junction with the body of the premaxilla. The latter, as has already been pointed out, is much more conspicuous than in Calyptomena and terminates in a doubly crescentic free edge synchronously with the palatines. Thus a relatively enormous oblong space is enclosed. In Corydon these features are still more exaggerated, the " elbow" is also more strongly marked. In broadness and the truncated form of the shaft of the palatines, the more specialised Eurylsemidse recall the Podargidse, wherein the body of the premaxilla is still more developed and the truncation of the palatine distally more marked. Both in the specialised Eurylsemidse and the Podargidse the truncation of the vomer appears to have been brought about to facilitate the movements of the nasal hinge, which in both types lies immediately above the anterior ends of the palatines, while in the more generalised Calyptomena, which lacks a nasal hinge, the palatines run far forwards. The pterygoid in Calyptomena (PI. II. fig. 2 a) is a long, slender, rod-shaped bone, laterally compressed, and perforated by a pneumatic foramen at its articulation with the quadrate. At its anterior end it meets its fellow of the opposite side in the middle line ; and immediately sends upwards and forwards a sub-crescentic plate which, embracing the parasphenoidal rostrum by its plane surface, affords attachment along its inferior border to the vomer. Late in life the articulation with the vomer is succeeded by anchylosis. Certain points concerning the morphology of the end of the pterygoid will be discussed in the section dealing with the nestling skull (p. 43). In Chasmorhynchus the anterior ends of the pterygoids do not meet in the middle line but impinge instead directly against the parasphenoidal rostrum, forming therewith a pedate articulation, which is largely augmented by " liemipterygoid " elements |
