288 MR. W. p. PYCRAFT ON TBfe [^V^- 1^' 



form, with the nasal bones, a more or less perfect fronto-nasal 

 hinge, see also p. 291. There is no transverse hinge as in 

 Microhierax or in Parrots. 



The Maxillo-Jugal Arch. 



The maxilla is indistinguishably fused with the premaxilla. 

 The maxillo-palatine processes have slowly incieased in size so as 

 to convert what -was originally a schizognathous into a desmo- 

 gnathous palate. M^iny intermediate stages in the course of this 

 transformation have been preserved and will be discu^ssed forth- 

 with. 



In the study of the transition of the palate fi-om the schizo- 

 gnathovis to the desmognathous type, we will commence with 

 Elanus : this foi'm being regaixled by Di-. Suschkin as exhibiting 

 more primitive chai'acters than any other Accipiti-ine bird. 



In Elanus then (PI. XXXI. fig. 2) the maxillo-palatine pro- 

 cesses turn inwards in the form of a pair of small, veiy pneumatic, 

 hamulate processes. Although they hem-in the vomei- on either 

 side, they do not extend so far inwai-ds as to touch it. Distad 

 of the vomer they ai-e hidden by the palatines, and thus leave 

 a large median palatal vacuity exposing the nasal septum above 

 and lying in the middle line. The maxillo-palatine processes 

 themselves are pierced, laterad of the palatines, and between 

 these and the tomium, by a large foramen. The palate, however, 

 of Elanus is not, I think, to be regarded as pi-imitive, but 

 specialized (see p. 313). Circaetus (PI. XXXI. fig. 4) is also schizo- 

 gnathous, and pi'obabiy i-epi-esents the intermediate type of palate 

 which has given rise, by specialization, in one dii-ection to the 

 palate such as is found in Elanus and the Oathartse, and in the 

 other to such as obtains in the Vultures and Falconidse. 



In Aquila (e. g. A. chrysaetos, A. audax), Spilo7'nis, and Thras- 

 aetus harpyia we find the maxillo-palatines greatly increased in 

 size antero-posterioi'ly, and extending inwards mesiad of the 

 palatines : so much so as to almost completely fill up the space 

 between them. The nasal septum is now visible only through a 

 narrow palatine clink. This increase in bulk has now caused the 

 maxillo-palatines so nearly to approach one another, that they 

 almost, if not quite, touch. But they are yet distinct, and the 

 palate must accordingly be regarded as schizognathous. 



In Serpentari'us they touch throughout the greater part of their 

 length, concealing the nasal septum (PI. XXXI. fig. 7). 



Indirect desmognathism, brought about by the downward 

 extension of the nasal septum, obtains in the majority of Accipitres, 

 and can best be studied in such forms as Elanoides, Pandion, 

 Vultures. In Gypa'etus and Neophron, for example, the maxillo- 

 palatines do not meet in the middle line, and but for the nasal 

 septum would be bounded anteriorly by a large palatal vacuity 

 as in Gathartes. 



Direct desmogiiathism is pei'haps only found in Falconidse. 



