186 ELEMENTS OF ORNITHOLOGY. 
remain separate from each other and from a vomer which does 
not taper, but is broad and truncated anteriorly, is distinguished 
as an Aiyithognathous skull, and such a one exists in the 
Sparrow and the Raven (fig. 152). A Dromeognathous skull 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. 
Lhe 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. For when the beak is opened and the 
lower jaw lowered, pressure is thereby exerted on the quadrate 
bone, which is almost always more or jess moveable. Con- 
sequently when it is pushed forwards by the depression of the 
lower juw, it simultaneously pushes forwards on each side the 
quadrato-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 
