1902.] OSTEOLOGY OP THE PALCONIFORMES. 317 



gnathism). The various transitional schizognathous types whicli 

 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 oi'ders has been 

 independently acquired by the modificatfon 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 Palfeognathse. The movement of the palatines towards 

 the mid- ventral line, whereby they come to undeiiie the distal 

 ends of the pterygoids, has caused the latter to segment and the 

 formation of a pseudo palato-pteiygoid joint. The segmentation 

 of the pterygoids and the fusion of the distal segments thereof 

 with the palatines relieved them from their function of support- 

 ing 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 with the palatines. 



2. A lengthening of the palatines, by their forward growth 



beneath the maxillo-palatine processes, with which they 

 originally vmited, to effect a union with the premaxilla ; 

 and a change in their position by the movement inwards 

 to meet in the mid-venti-al 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 svippoi't 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. 



