I 86 ELEMENTS OE OENITHOLOGT. 



remain separate from eaeh other and from a vomer which does 

 not taper, but is broad and truncated anteriorly, is distinguished 

 as an ^githognathous skull, and such a one exists in the 

 Sparrow and the Eaven (fig. 152). A Dromceognaihous skuU is 

 one wherein the palatines and pterygoids do not join the rostrum, 

 but are separated from it by the vomer, or each pterygoid 

 articulates with a lateral outgrowth from the basi-sphenoid. 



The bones of the face are more or less moveable, as will be 

 .explained shortly. 



The lower jaw is formed of two lateral branches or rami, 

 which anchylose together anteriorly where they meet at what 

 is called the symphysis. The hinder end of each ramus is 

 expanded and presents above a concave articular surface for 

 junction with the quadrate bone., Often a process projects back- 

 wards beyond, this is called the angle or posterior angular process 

 or posterior articular process^ This may be upturned at the end, 

 i. e. recurved, or it may be abruptly terminated or, as it is called, 

 be truncated. Another process generally projects inwards from 

 the articular surface. This is called the internal angular 

 process. Another process may project upwards in front of the 

 articular surface, and such a structure is termed a coronoid 

 process. 



Each half of the mandible is made up of five bones. . 



In front is the dentary, next comes the angular with the 

 surangular above it outside the articular process, which is formed 

 by the articular, while on the inner side of the ramus towards 

 its middle is a small bone termed the splenial. There is often 

 a vacuity or fontanelle towards the middle of either ramus 

 between the dentary and the angular and above the splenial. 



The Movements of the Jaws. — The lower jaw of the bird moves 

 substantially as does our own, but the upper jaw is to a greater 

 or less degree moveable also. The delicate bony bars which con- 

 nect its solid apex with the cranium are to a certain extent 

 elastic, and that apex tends to be elevated by the mere action 

 of opening the beak. Por when the beak is opened and the 

 lower jaw lowered, pressure is thereby exerted on the quadrate 

 bone, which is almost always more or less moveable. Con- 

 sequently when it is pushed forwards by the depression of the 

 lower jaw, it simultaneously pushes forwards on each side the 

 quadrate- jugal bar, or " zygoma" (which unites posteriorly 

 with the quadrate externally), and also the pterygoid (which 

 unites with the quadrate on its inner side), and, through that 



