SKELETON. 



603 



four ribs there is an uncinate process, absent only in the 



horned screamers (Palamedeae). 



The skull has a rounded cranial cavity 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 basi-occipi- 

 tal, the two ex-occipitals, and 

 the supra-occipital. These 

 bound the foramen magnum 

 through which the spinal 

 cord passes. The basi-occipi- 

 tal forms most of the single 

 condyle on which the skull 

 rotates. 



The top of the skull is 

 formed from the paired parie- 

 tals, frontals, and nasals, the 

 last being small and in part 

 superseded by the upward 

 extension of the premaxillae. 

 The line of the upper jaw 

 consists of premaxilla, small 

 maxilla, jugal, and quadrato- 

 jugal, the last abutting on 

 the movable quadrate. 



Of the membrane bones 

 on the side of the skull, the 



FIG. 209. Under surface of 

 Gull's Skull. (From Edinburgh 

 Museum of Science and Art. ) 



lachrymal in front of the 

 orbit, and the squamosal 

 above the quadrate, are the 

 most important. 



On the roof of the mouth 

 the basisphenoid, which lies 

 just in front of the basi-occipital, is covered over by a 

 membrane bone the basi-temporal. In front of this is a 

 sharp " basisphenoidal rostrum," or parasphenoid, also a 

 membrane bone. Articulating with the quadrate and with 



c., Condyle ; 3./., basi-temporal; b.s., 

 basi-sphenpidal rostrum ; //., pterygoid ; 

 bet., palatine ; 7>. , vomer ; p^mx., pre- 

 maxilla ; mx., maxilla; /., jugal; q.j., 

 quadrato-jugal ; q., quadrate. 



