BIRDS. 



335 



median line forming a bony roof across the palate (Fig. 324). 

 In the schizognathous skull there is a gap between the max- 

 illopalatine processes, and another between them and the vomer 

 when the latter is present, the latter bone being pointed in 

 front. In the aegithognathous forms the vomer is truncate in 

 front and cleft behind, the rostrum being embraced between 

 its forks. In the saurognathous skull the vomer is paired. 



The hyoid arch is but slightly devel- 

 oped ; the first branchials, on the other 

 hand, may be large. These two form 

 a Y-shaped structure, the stem consist- 

 ing of an anterior os entoglossum (paired 



Fig. 327. Skull of quail, schiz- 

 ognathous type. PL, maxillopala- 

 tines ; PT, pterygoid ; Q, quadrate ; 

 R, rostrum ; V, vomer. 



Fig. 328. Sternum and pectoral girdle 

 of Casuarius, after Parker, c, coracoid ; 

 cl, clavicle ; pc, procoracoid ; s, scapula. 

 Cartilage dotted. 



in origin and possibly representing the hyoid arches) and a 

 posterior basihyal from which arise a pair of cornua (ist bran- 

 chials), which are usually made up of several segments. Ex- 

 tending backwards from the basihyal, between the cornua is a 

 'urohyal,' in reality a basibranchial. 



The pectoral girdle is well developed except in the flightless 

 birds, and in some moas apparently it was entirely absent. The 

 coracoids are large, the procoracoids rudimentary or absent. In 

 most ratite forms the clavicles are absent ; in all other birds they 



