ft 



Chap. VIII.] THE SKELETON. 153 



y. 



a circle of small imbricating bones, the sclerotic plates, is developed 

 is enclosed in the large rounded orbit. This is bounded behind/v 

 by the anterior wall of the brain-case; on its inner side %~^. 

 the inter-orbital septum ; and anteriorly by the nasals and the 

 lachrymals (lc.), small bones with a sharp downward-directed 

 process, and not ankylosed to the skull even in old birds. (The 

 sharp process internal to that of the lachrymal is part of the 

 ethmoid bone.) Below, the orbit is bounded internally by the 

 palatines and pterygoids (pi. pt.), and externally by a slender 

 bar composed of the maxillae (mx.\ the jugal (ju.), and the 

 quadrato-jugal (q. j.), which is attached by ligament to the 

 quadrate bone (qu.). 



(5.) The Maxillary and Palatal Region. There are no tooth- 

 bearing bones. The pre-maxillae (p. mx.) 9 which form the 

 greater part of the upper mandible, are, in the fresh skull, en- 

 sheathed in horn. Each has long slender nasal processes 

 running up to the frontals internal to the nasals, and stout 

 maxillary processes, each of which sends inwards a palatal shelf, 

 to which the palatine is attached in the adult. The maxillae 

 (mx.) at their anterior ends send inwards flattened maxillo- 

 palatine processes which nearly meet in the middle line ; for the 

 rest of their length they are slender. The palatines (pi.) are 

 also slender for three-fourths of their length ; but in the 

 posterior fourth they send inwards curved scroll-like processes 

 which meet in the middle line beneath the rostrum. Their 

 hinder extremities articulate with the pterygoids (pt.\ short, 

 stout, mallet-shaped bones, the handles of which pass outwards 

 and backwards to articulate with the quadrate. The quadrate 

 (qu.) is a large irregular somewhat Y-shaped bone. By one 

 limb of the Y it articulates with the dorsal part of the tympanic 

 cavity (h. q.). The other limb of the Y is seen at a. p. q. 

 (Fig. 48, B.), partially hidden by the pterygoid. At the foot 

 of the stem there is a condyle for the articulation of the lower 

 jaw, near which it articulates with the quadrato-jugal (q. j.). 



(6.) The Mandible. The two rami ankylose at the symphysis, 

 and the component elements are more or less completely fused 

 together in the adult. In the chick, however, each ramus is 



