246 THE ANATOMY OF VERTEBRATED ANIMALS. 



a complete bony roof across the palate. In the Sc7iizognath(^ 

 (Fig. 82), and ^gitliognatlim^ the maxillo-palatines remain 

 quite distinct both from one another and from the vomer. 



The quadrato-jugal is usually a slender rod of bone, the 

 liinder extremity of which presents, on its inner side, an artic- 

 ular head which fits into a fossa in the outer face of the distal 

 end of the quadrate bone. 



The palatine bones are generally long and concave on their 

 palatine faces. In front, they pass beneath (i. e., on the ven- 

 tral side of) the maxillo-palatines and unite with the premax- 

 illse, sometimes by a squamous suture, sometimes by anchy- 

 losis, rarely, as in the Parrots, by a flexible joint. Posteriorlv, 

 they always unite with the pterygoids. In most birds, the 

 palatines converge, posteriorly, toward the basi-sphenoidal 

 rostrum, and unite with it by an articular surface, which allows 

 of a sliding motion of the palatines upon the rostrum. Such 

 an articulation does not exist in ^cditm^ or in the Tinamous, 

 among the Carinatce. In these (with the exception of 

 Struthio), the palatines are, as it were, borne off from the ros- 

 trum by the divergent ends of the great vomer, and the dispo- 

 sition of the parts is more lacertilian than in other birds, 

 The outer, or posterior, end of the pterygoid bone presents a 

 fossa for an articular head, which is developed upon the inner 

 side of the distal end of the quadrate. The inner, or anterior, 

 ends of the pterygoids meet in almost all birds, and may be- 

 come articulated with the basi-sphenoidal rostrum. In all em- 

 bryonic birds, in all the Jxatitm^ and in many Carinatce^ such 

 as the TinamfiomoTpJim^ Charadriomorplim^ Alectoo'otnorphce, 

 Perlsteromorphoe^ Chenomorpjfim^ longer or shorter processes 

 extend from the basi-sphenoid, and present terminal articular 

 facets to corresponding facets upon the inner sides of the 

 pterygoids. These are hasi-pMrygoid processes, similar to 

 those which occur in Lacertilia and some Ophidia, 



The quadrate bone is almost always movable upon the 

 skull, articulating with the prootic, alisphenoid, and squamo- 

 sal, by a single, or double, head. The distal head articulates 

 with the mandible below, the quadrato-jugal on the outer, and 

 the pterygoid on the inner, side. Hence, when the ethmo- 

 nasal joint is developed, any forward movement of the distal 

 end of the quadrate, such as must take place when the mandi- 

 ble is depressed by the digastric muscle, causes the maxillo- 

 jugal bar to thrust the premaxilla upward and forward ; the 

 palatine and pterygoid bones, at the same time, sliding for- 

 ward upon the rostrum of the basisphenoid. Thus it comes 



