370 SKELETON OE THE FOWL 



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 premaxiUa. 



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 quad- 

 rate 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 

 which it can slide. 



ii. The palatine 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 premaxiUa. 



iii. The premaxiUa is a triradiate bone, the anterior 

 part of which is ankylosed with its fellow in 

 the median plane to form the tip of the beak, 

 while the three processes diverge backwards. 



The ascending or nasal process, which is 

 much the longest of the three, is a long 

 slender bar of bone, which runs backwards 

 and upwards, closely applied to its fellow of 



