SKULL BIRDS 



179 



septum, and is usually visible between the palatines. These latter 

 are long and flat, and usually have an articular surface which forms 

 a sliding joint on the rostrum, while the posterior part articulates 

 with the pterygoid, the anterior being connected immovably with 

 the premaxilla (except in Ratites) and borders the choana. The 

 pterygoid articulates with the quadrate and sometimes with the 

 basipterygoid process of the alisphenoid, sometimes with the rostrum 

 in front. 



The palatal structure has been invoked as a basis of classification of birds. 

 Originally four types were recognized (Huxley): dromaeognathous, schizogna- 

 thus, aegitognathous and desmognathous. More recently birds have been 



Fig. 193. — Palatal regions of (.4) Corvus, (B) Dromceus, C, Rhea, and (D) Rissa 

 (Pyeraft, 'or), h, hemipterygoid; m, maxilla; pa, palatine; pm, premaxilla; pt, ptery- 

 goid; q, quadrate; v, vomer. 



separated into two great groups, each with subdivisions. In dromaeognaths 

 the united vomer is large and overlaps (ultimately fusing with the anterior 

 ends of) the pterygoids so that motion is impossible between them. The 

 pterygoids and palatines do not meet the rostrum, and the palatines, which 

 do not meet the premaxilla?, articulate with the maxillae. Dromceus (fig. 193, B) 

 has the anterior end of the vomer entire, concealing the rostrum, while the broad 

 hinder end of the palatine meets the lateral end of the vomero-pterygoid (PalcC- 

 ognathae). From this the tendency is for the palatines to meet ventral to the 

 vomero-pterygoid junction (pterygoid sometimes meeting only vomer; palatine 

 and vomer in others) while a division of the vomer in front allows the rostrum 

 to be seen (true DromEeognaths). In Neognathas the palatines meet behind 

 in the middle line, supporting the vomer between them, while there is a moveable 



