THE SKULL. 411 



and are closely connected with processes of 

 the premaxillcB. 

 ii. The vomer is a slender median bony rod, which 

 lies below the hinder part of the olfactory 

 capsules, and immediately in front of the 

 rostrum. It is paired in some birds. 



b. The upper jaw. The bones of the upper jaw, as 

 seen from the ventral surface, form on each side 

 two bony arcades, which are fused together in 

 front to form the beak, and are closely approxi- 

 mated behind, but widely separated from each 

 other along the greater part of their course. 

 The inner arcade is formed by the pterygoid and 

 palatine bones, which articulate with the rostrum : 

 the outer arcade consists of the slender sub-orbital 

 bar and the premaxilla. 



The upper jaw is connected with the anterior 

 end of the frontals, and with the mesethmoid. 

 Posteriorly, it is slung up to the side of the skull, 

 just in front of the tympanic cavity, by the qua- 

 drate bones, 

 i. The pterygoid is a short stout bone, forming the 

 hinder part of the inner arcade. It articu- 

 lates at its outer and posterior end with the 

 inner surface of the quadrate, and at its 

 inner and anterior end with the rostrum, along 

 whicli it can slide, 

 ii. The jmlatine is a slender horizontal bar of bone 

 lying in front of the pterygoid, and forming the 

 greater part of the inner arcade. Behind, it 

 articulates with the pterygoid, and is expanded 

 into a broad lamella, which articulates with 

 the rostrum along its inner edge. In front, 

 the palatine is wedged in between the maxilla 

 and the premaxilla. 

 iii. The premaxilla is a triradiate bone, the anterior 

 part of which is ankylosed with its fellow in 



