AND CLASSIFICATION OF THE FOSSIL REPTILIA. 
247 
orbito-sphenoid, placed at the back of the orbit, and perforated. Thus, the sides of 
the brain-case converge as they extend forward, till they merge in the vertical median 
septum which may be formed at its base by a flat median process of the pterygoid, 
on which is placed the pre-sphenoid, similarly compressed from side to side and 
elongated; above this bone succeed vertical plates of the parietal and frontal bones ; 
and anteriorly these elements are prolonged by the ethmo-vomerine plates described 
by Professor Huxley. 
Fig. 4. 
]}re-f7'oiitoci. 
lachrymaZ. 
max, 
inalar: 
Plan of the Upper Surface of the Skull of Dicynodon. 
The palate in Dicyuodonts is characterized by being formed mainly by the pterygoid 
bones. They are large horizontally extended plates, which meet in the median line 
and rest upon the basi-sphenoid, much as in Chelonians, but three processes appear to 
be given off, of which Chelonians show no evidence. First, a process is directed 
outward and backward'to the quadrate bone, and is separated from the mass of the 
bone behind it by a notch. Secondly, from the anterior corner a long bar of bone is 
produced forward and outward to meet the maxillary bone behind the great tooth ; 
and so as to make the external margin of the pterygoid concave. Between these 
anterior bars a pair of smaller processes is given off, which soon converge as they 
extend forward, and are developed into a vertical median plate which underlaps the 
pterygoid, and extends forward to meet the vomer, but soon rises so as to disappear 
from the horizontal plane of the palate. The palatine bones extend along the whole 
length of the anterior bars of the pterygoids. They are narrow, splint-like bones at 
first, on the inner sides of the maxillary bars of the pterygoid, and widen as they 
extend forward into the maxillary, where they converge toward the median line, but 
are commonly separated from each other by the vomer. A process from the palatine 
