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Show 1902.] OSTEOLOGY OF THE FALCONIFORMES. 313 the Falconiform palate must be our justification for pursuing this matter- a little further. The palate of the Cathartse is undoubtedly of an extremely specialized type, but traces of a like modification are not wanting in a direction where hitherto they have not been looked for-to wit, in the Accipitres proper. The palate of Elanus, as we have already described, is schizognathous, a fact first pointed out by Shufeldt; but the schizo-gnathism is of a specialized character, being due to the extreme reduction of the maxillo-palatine processes. If the nasal septum in the skull of Elanus be examined, it will first of all be remarked that it is more complete than in the Cathartae, and next that, near its posterior inferior angle, it gives off a pair of small horizontal processes, resembling those of Cathartse, but relatively smaller; these almost touch the maxillo-palatines. A little increase in the size of these spurs, and the reduction of the anterior portion of the septum would give us the Cathartine palate. Thus, then, the palate of Elanus must be held to represent the high-water mark of specialization in the direction of schizognathism in the Accipitres. It is probable that the palate of Circaetus-or rather the maxillo-palatines-represents the intermediate type from which the extremes of schizog- and desmognathism in the group have been derived. Furthermore, it may profitably be compared with the palseognathine maxillo-palatine of, say, the Tinamous. It must be remembered that the great feature of the palseognathine palate is the enormous size of the maxillo-palatines. In the highly specialized Tinamus this is much reduced, and in general shape is not unlike that of Circaetus, but lacks its vertical plate of spongy tissue. It is important that the intermediate character of the palate of Circaetus should be recognized, otherwise we commit ourselves to the admission that the desmognathous palate of forms like the Falconidse or Aquila, for example, were developed by the resuscitation of an almost defunct organ. In Circaetus, then, the maxillo-palatines are represented by a pair of vertical plates of spongy tissue nearly meeting in the mid-ventral line. They run backwards nearly as far as the antorbital plate (prefrontal) ; and forwards, then inwards towards the tomium, so as to leave a palatal vacuity exposing the nasal septum as in Elanus. Reduction of this type of maxillo-palatine gives us the highly specialized type of Elanus, its further increase the type seen in the Falconidse, notably through Milvago to Polyborus and Ibycter (PI. X X X I I I . figs. 3, 5), wherein the maxillo-palatines have attained a relatively enormous size. In the Fcdconince we meet with an exactly parallel series, passing through Harjxc to Herpetotheres (PI. X X X I I I . figs. 2-4). In the higher Falcons an increase in size of the anterior nasal chamber, eventually, m Fcdco, developing into a much inflated ossified bulla, has brought about'a considerable reduction in the size of the maxillo-palatine processes; the fenestrated bullae, seen in such perfection in PROC. ZOOL. Soc-1902, VOL. I. No. X X I 21 |
