AVES. 9 



ncludes all living birds in which the vertebrae supporting the 

 rectrices have become so abbreviated that the tail-feathers have 

 to be arranged fan-wise on either side of a fused mass of bones 

 known as the " pygostyle." 



As regards the Neorniihes, the palate affords a much more satis- 

 factory basis of division than the sternum. According to this, 

 living birds are divisible into two further groups, the Prtlceognaihce 

 and Neoynathce, the former in substitution for the Ratitce and the 

 latter for the Carinatce. 



In the PalcEoynatlia} the vomer is large, and articulates by 

 squamous suture with the pterygoid, while the palatine is applied 

 to the outer margin of the vomero-pterygoid articulation. 



In the Neognatlice the palatines have shifted inwards, under 

 the vomero-pterygoid articulation, to meet one another in the 

 median line. The pterygoids, in early post-embryonic life, undergo 

 a striking process of segmentation, inasmuch as that portion of 

 their shafts which rests upon the proximal end of the palatine suaps 

 off, as it were from the main shaft, and fuses with the palatine. 

 Later, at the point of fracture a cup-and-ball joint is formed, 

 affording the strongest possible contrast with the squamous 

 suture found in the Patasognatkce. 



Where the vomer still retains some semblance of its former 

 size, its proximal bifurcated end may just reach the extreme tip 

 of the anterior end of the pterygoid, but it now depends for its 

 support not upon the pterygoid, but upon the palatine, as, for 

 example, in the Penguins. But among the Neognatltce the vomer 

 displays a striking series of stages in degeneration., becoming more 

 and more divorced from the pterygoid, until it finally assumes 

 the form of a minute nodule of bone, and at last, in the Gallince, 

 it becomes a mere spicule of bone held by a few tendinous fibres 

 to the anterior border of the expanded ends of the palatines, and 

 in some, as in the Falconidce for example, vanishes altogether. If 

 nothing were known of the early post-embryonic developmental 

 stages of the Neoc/nathine vomer, it would have been impossible 

 to divine that the Neognathine was a direct derivative from the 

 Palceognatliine palate. 



These two orders, the Pcilceognatlice and Neognatlice, must be 

 divided further, for the Class Aves, in the course of its evolution, 

 has split up into a A r ast number of different forms. The genetic 

 relation of these forms or types to one another, and the precise 

 affinities of the individual members of the various groups, should 

 as far as possible find expression in any system of classification. 

 These divisions may be known as Orders, which are again divided 

 into Sub-Orders, Families, Genera and Species. 



