OCR Text |
Show 2 6 6 MR. W. P. PYCRAFT ON THE [Mar. 17, Among the Cuculi, the least specialised palate is probably to be found in Coua and Eudynamys. In Coua the maxillo-palatine processes are widely separated and spongy in character; the consequent palatal vacuity is filled by the nasal septum, which is also spongy in character, and, fusing with the maxillo-palatine on either side, forms an indirectly desmognathous palate. Eudynamys closely resembles Coua in this respect, but the bony tissue is less spongy, and the fusion between the palatine processes and nasal septum is more complete. Cue ulus, G uira, and Centropus resemble Eudynamys. Further specialisation of the palate is seen in the still further obliteration of the boundaries between the maxillo-palatines and the nasal septum, and the tendency to shorten and broaden the palatines. Forms like Geococcyx and Rhinococcyx show how these modifications have come about, whilst in Bhamphococcyx we may see the maximum development of these peculiarities. In the Musophagi the maxillo-palatines never appear- to completely coalesce in the middle line, nor does the nasal septum descend to the level of the ventral surface. The palate is nevertheless desmognathous, since this septum fuses with the dorsal surfaces of the maxillo-palatines. No separate elements can be distinguished in the quadrato-jugal bar. In the Cuculi the quadrato-jugal bar is almost or quite continuous with the tomium of the maxilla : in the Musophagi, on the contrary, it rises considerably above the level at its distal end. This difference is due to the fact that in the Cuculi the floor of the maxillo-palatine process lies low, being only just raised above the palatines at its postero-external angle, whilst in the Musophagi this region is raised high above the palatines. The Vomer, Palatines, and Pterygoids. The vomer is absent in the Cuculi, vestigial in the Musophagi. In the latter group it is spicular in form and fused with the palatines, which it joins by means of a pair of very short limbs. Anteriorly it touches the nasal septum. The palatines, in the Cuculi, vary in shape. In the less specialised forms, such as Eudynamys, Coua, Guira, they are moderately long, and exposed slightly outwards. Anteriorly, from the level of the forward face of the antorbital plate to the point of fusion with the maxillo-palatines, the shaft of each is rod-like; cephalad of this point the bone spreads out into a moderately broad blade, the postero-external angles of which are rounded off, whilst the mesial border is produced ventrad to form a more or less pronounced keel. In Cuculus there is but little difference in the width between the anterior and posterior moieties, and the shaft is nearly straight. In the heavy-billed forms like llliamphococcyx and Rhinococcyx the palatines are relatively shorter, and have the maxillo-palatine extremity laminate instead of rod-like. The skull of Scythrops, I regret to say, is not contained in the National Collection. |