334 



CLASSIFICATION OF VERTEBRATES. 



FlG. 325. Illustrating the hinging and movements of the maxilla and other 

 bones in the birds ; modified from Boas. J, jugal ; A 7 , nares ; O, orbit ; P, palatine ; 

 PT t pterygoid ; Q, quadrate. 



The quadrate is freely movable. In the floor of the skull appear 



three bones which in part replace the parasphenoid of the ich- 



thyopsida. These are, behind, a 

 pair of basitemporals (fused in 

 the adult), and, in front, a me- 

 dian rostrum. The rami of the 

 lower jaw are anchylosed at the 

 symphysis. 



The relations of palatines, 

 pterygoids, and vomers show 

 many variations, and have been 

 used as a basis of classification 

 of birds. Although this classi- 

 fication has not obtained accept- 

 ance, the conditions are fre- 

 quently used as characters, and 

 may be described here. 



In the dromaeognathous skulls 

 the vomers form a broad bone 

 separating the rostrum from the 

 palatines (Fig. 326), and occa- 

 sionally from the pterygoids. In 

 all others the palatines and 

 pterygoids articulate with the 

 rostrum, but they differ in other 

 respects. In the desmognathous 

 type the vomer is more or less 

 FIG. 326. Skull of ostrich (dro- rudimentary while the maxillo- 



mjeognathous type). //, palatine; pt, . 



pterygoid; r, rostrum; , vomer. palatine prOCCSSCS Unite in the 



