244 PROFESSOR H. G. SEELEY ON THE STRUCTURE, ORGANIZATION, 
Summary of the Structure of the Dicynoclont Skull. 
The same plan of structure is found in all the skulls of Dicynodonts which I have 
been able to compare, archough the proportions of the different parts of the head vary 
in the genera. The post-orbital region may be greatly elongated, as in Dicynodon 
leoniceps, when the parietal area is usually an angular crest, or the transverse expan¬ 
sion may be considerable, and the parietal region flattened and tabular, as in 
Dicynodon tigricep)^. The nares may approach near to the extremity of the snout, 
as in some species of Oudenodon, or the pre-maxillaries may have a great anterior 
development, giving the nares a backward position, as in Ptychognathus. But, 
although the relative size and shape of every bone become modified in harmony with 
these modes of growth, the plan on which they are arranged never varies, so far as I 
have been able to ascertain. This plan consists in a solid jaw, from which a vertical 
longitudinal median plate is prolonged backward, where it divaricates to contain the 
small brain. This wedge is terminated posteriorly by a more or less vertical occipital 
plate. Inferiorly the back of the squamosal region is connected with the jaws by 
longitudinally extended slender bars, which form the palate. Laterally the squamosal 
extends towards the maxillary, forming a single lateral arch behind the orbit. 
Superiorly the anterior part of the head is more or less flat, and horizontally extended 
parallel to the palate. 
Fig. 2. 
The occipital plate may either be transversely extended and vertical, or may have 
its lateral halves directed outward and backward. It includes a rounded occipital 
condyle, which is formed by the basi-occipital and the two ex-occipitals, which are 
