602 



BIRDS. 



four thoracic ribs there is an uncinate process, absent 



only in the S. American 

 screamers (Palamedea?). 



The skull has a rounded 

 cranial cavity, large orbits, 

 and a narrow beak, which 

 is mostly composed of 

 the premaxillae. All the 

 bones are fixed except 

 the quadrate, lower jaw, 

 columella, and hyoid. 

 The surface is polished ; 

 the sutures are obliterated 

 very early in life. 



The back part of the 

 skull is formed by the 

 basioccipital, the two ex- 

 occipitals, and the supra- 

 occipital, surrounding the 

 foramen magnum. The 

 basioccipital forms most 

 of the single condyle. 



The roof of the skull 

 is formed from the paired ' 

 parietals, frontals, and 

 nasals, the last being 

 small and in part super- 

 seded by the upward ex- 

 tension of the premaxillae. 



The line of the upper 

 jaw consists of premaxilla, 



Fig. 262. -Under surface of gull's skull. sma11 maxilla, jugal, and 

 —From Edinburgh Museum of Science quadrato-jugal, the last 



andArt - abutting on the movable 



t.j Condyle; bt., basitemporal ; &.s., basi- nnnrlntp 

 sphenoidal rostrum; ft., pterygoid; pa.., 4 U " UI " C ' 



palatine; v., vomer; /.»., premaxiiia; Of the membrane bones 

 j^T^rie^ "*' quadrat °" on the side of the skull, 



the lachrymal in front of 



the orbit, and the squamosal between the quadrate and 



the parietal, are the most important. 



On the roof of the mouth, the basisphenoid, which lies 



