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Show 1902.] OSTEOLOGY OF THE FALCONIFORMES. 317 gnathism). The various transitional schizognathous types which occur with considerable frequency, and sporadically, indicate the steps by which these two forms of desmognathism have been acquired. The presence of the hemipterygoid element in all save the Falcons is a point of considerable interest, serving not only as an additional index of the high degree of specialization which the family has undergone, but also to show how a character common to the members of several widely different orders has been independently acquired by the modification of a common plan of structure. As I have recently pointed out, the Neognathine (Carinate) palate has been derived directly from the dromseognathous found only in the Palaeognathae. The movement of the palatines towards the mid-ventral line, whereby they come to underlie the distal ends of the pterygoids, has caused the latter to segment and the formation of a pseudo palato-pterygoid joint. The segmentation of the pterygoids and the fusion of the distal segments thereof with the palatines relieved them from their function of supporting the vomer and threw the work upon the palatines. As a consequence atrophy of the hemipterygoid ensued; indeed, in all the members of some sub-orders, e. g. Anseres, Galli, and in the Falcones, it has been entirely suppressed. When present, save in a few exceptional cases, it has lost all actual connection with the vomer, which is borne entirely by the palatines. The evolution of the Neognathine palate has effected the following changes :- 1. A shortening of the pterygoids, by the segmentation of their distal ends and the fusion thereof wrth the palatines. 2. A lengthening of the palatines, by their forward growth beneath the maxillo-palatine processes, with which they originally united, to effect a union with the premaxilla ; and a change in their position by the movement inwards to meet in the mid-ventral line. 3. A reduction in the size of the vomer, resulting frequently in its complete suppression. But besides changes of position in their relative lengths, the pterygoids have also undergone a change of function, since these bones now serve as mere backward extensions of the palatines, their original function, the support of the vomer, being transferred as aforesaid to the palatines. Similarly, the palatines have assumed new functions, in addition to the support of the vomer. They occupy, functionally, with the now subordinated pterygoids, the place of the conspicuous submedian vomero-pterygoid bar of the Palseognathine skull, wherein, it will be remembered, they formed but little more than an appendix to the pterygoid. |
