MORPHOLOGICAL REVISION OF THE SUBORDER. 



153 



posterior than the inner. The long axis of the condyles is inclined somewhat inward. 

 The outer condyle is extended backward, as in Dimetrodon^ forming a sort of shelf on 

 which rests the lower end of the quadrato-jngal. 



The qiiadrato-jitgal and prosqitamosal occupy the same relative positions as in 

 Dimetrodon. The first rests against the posterior edge of the quadrate and overlies 

 the posterior edge of the prosquamosal. There are indications that a quadrate foramen 

 was present, but it is closed in the specimen, perhaps by pressure. Superiorly, the 

 quadrato-jugal passes below the lower ends of the squamosal and a second bone, the 

 epiotic (?). The anterior end of the prosquamosal is broken away, but it reaches up 

 as far as the upper edge of the quadrate, touching the lower end of the squamosal. 



The squamosal is a thin and slender element convex in curvature, which joins 

 the parietal above and the quadrato-jugal and the prosquamosal below. At its lower 

 end a wide process started forward toward the postorbital, but this is broken so that 

 its anterior connections can not be made out. The j^rocess evidently is a portion of a 

 bridge across the temporal vacuity; Cope considered that there was but one such 

 bridge and that the animal had a single temporal arch, but the condition of the speci- 

 men makes probable the possibility of the presence of a second arch below. 



Fig. 68. — Diagram of the lateral surface of the skull of Edaphosaurus pogonias. 

 Fig. 69. — Diagram of the posterior surface of the same. 

 Lettering as in figs. 66 and 67. 



Epiotic if) : Below the parietal and interparietal and above the posterior wall of 

 the cranial cavity is a pair of slender bones that curve outward and downward ; lying 

 next to the lower edge of the squamosal they extend outward and downward until 

 they touch the upper ends of the quadrato-jugal. These bones are in the exact posi- 

 tion of the epiotics, and there is little doubt that they are homologous with the same 

 bones in the Cotylosauria and Stegocephalia. They do not occur in the other families 

 of the suborder. 



The posterior surface of the cranium is formed by a single mass of bone, the 

 sutures between the basioccipital, siipraoccipital, exoccipifa/s, and the paroccipitals are 

 not distinguishable. The plate is partly obscured in the specimen by the crushing 

 which has forced the parietals with the interparietal and the epiotics down over it as 

 far as the foramen magnum. The paroccipital processes extend outward nearly to the 

 quadrate. The occipital condyle is relatively broad and oval in outline with no pit 

 marking the position of the anterior end of the notochord. 



The basisphenoid has the same form as in Dimetrodon^ but is relatively longer. 

 There is a strong parasphenoid process, well-developed articular faces for the ptery- 

 goids and a large pit on the lower surface. 



