372 SKELETON OF THE FOWL 



In front it extends forwards as far as the 

 maxilla, being overlapped for a considerable 

 part of its length by the jugal. 



c. The mandibular arch is divided into two portions 

 of very unequal length, placed almost at right 

 angles to each other. The proximal part is the 

 quadrate bone, which connects both the upper 

 and lower jaws with the cranium : the distal por- 

 tion, forming the lower jaw, is of much greater 

 length, is fused with its fellow in front, and is 

 cotaposed of several bones firmly united together. 



i. The quadrate, which forms the suspensorium, is 

 a stout triradiate bone. Its proximal or dorsal 

 arm articulates with a cup-like depression in 

 the squamosal, at the anterior and upper border 

 of the tympanic cavity, between this and the 

 base of the zygomatic process. 



The distal or ventral arm, which is the 

 stoutest of the three, is expanded transversely 

 at its lower end, and forms the articular 

 surface for the lower jaw : it also articulates 

 at its outer edge with the quadrato-jugal, and 

 along its inner margin with the pterygoid. 



The third or anterior arm of the quadrate 

 is a more slender process, which projects for- 

 wards and inwards into the hinder part of the 

 orbit, lying parallel to and above the pterygoid 



ii. The lower jaw, or mandible, is a long, laterally 

 compressed plate of bone, thickened and 

 expanded at its hinder end, where it articu- 

 lates with the quadrate, and firmly united 

 with its fellow in the median plane in front. 

 Like the upper jaw, it bears no teeth, but is 

 covered by a horny epidermic sheath. 



The mandible really consists of five bones 

 on each side, one of which is developed in 



