142 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



On either side of the skull, parallel to the frontals and nasals, are ele- 

 ments running from the anterior edge of the orbit to the posterior edge 

 of the nasals; a descending process, near the anterior end, forms the pos- 

 terior edge of the nares and joins the maxillary below. These bones form 

 the side "of the facial region and have been called lachrymals (Case) and 

 prefrontals (Williston) . 



The maxillaries are short and very slender. They form the lower border 

 of the nares and send a long splint back to a point below the middle of the 



orbit. 



The parietals are large plates forming the whole interorbital surface 

 of the skull, and are strongly convex from side to side. There is no trace 

 of a parietal foramen. 



The supraoccipital is a single median plate which extends downward 

 on the posterior surface to form the upper edge of the foramen magnum. 



On either side of the supraoccipital plate are large elements forming 

 the posterior angles of the skull; these were called squamosals by Case and 

 epiotics by Williston. Their homology seems uncertain. 



From the lower side of these elements, a projection for\vard carries 

 on its lower end the articulation for the lower jaw; it is certain that the 

 lower end represents the quadrate. The upper portion may or may not be 

 distinct; a partial suture was noted by both Williston and Case. The upper 

 part, called by Williston the squamosal, corresponds almost exactly to the 

 part called tympanic (Hoffmann) or paraquadrate (Gaup). The lower, 

 quadrate end of this composite bone becomes very slender and rod-like. 



The lower surface: A large flat bone forms the posterior surface of the 

 basicranium; this is considered to be a basisphenoid; anterioriy itis joined 

 by an equally broad element which terminates in a point anterioriy, the 

 parasphenoid. 



Anterior to the parasphenoid the separate elements can not be made 

 out. The teeth extend in an unbroken curve around the anterior edge of 

 the skull, and a second line of palatine (?) teeth withinthis follows neariy 

 the same curve. There is a great median, palatine vacuity. 



Broili reported the occurrence of gular plates lying between the lower 

 jaws, but Williston has given reasons for believing that these are the dis- 

 placed elements of a proatlas. 



Posterior surface: This is completely closed. There are distinct, exoccip- 

 ital condyles (Williston and Case); BroiU believes that there is a single 

 tripartite condyle, the lower portion formed by the basioccipital bone. This 

 he reports on the evidence of several specimens; Williston andCase, working 

 independently, with separate series of skulls, are of the opinion^ that the 

 condyles are paired and formed by the exoccipitals._ Broili's criticism of 

 Case's drawings showing the condyles does not take into account that the 

 condyles slant inward and upward; the greatest distance between the con- 

 dyles shown in the posterior view of the skull is greater than that between 

 the pordons of the condyles shown in the lower view, but it is the upper 

 ends of the condyles which show in the lower view, and the two drawings 

 coincide exactly. . 



The lower jaw is about two-thirds the length of the skull and is very 

 wide in the articular region. The angle projects considerably beyond the 

 quadrate. The dentary carries small conical teeth similar to those of the 

 maxillary. 



