96 A REVISION OF THE COTYLOSAURIA OF NORTH AMERICA 



teriorly, with the quadratojugal; it overlies the quadrate. The quadratojugal lies 

 on the outer side of the quadrate and frequently extends up behind it; the portion 

 which extends up behind the quadrate articulates with the posterior edge of the 

 prosquamosal. This is exactly the relation of the outer pair of posterior elements 

 in Captorhinns and the Pelycosauria. 



If we assume that this element covering the posterior and outer surface of the 

 quadrate in Captorhinus, Diadectes, and the Pelycosauria, and separated from the 

 quadrate by a foramen, is, in the last two, the quadratojugal, then we have in the 

 temporal region the full number of bones of the Stegocephalian skull; this bone 

 is in many forms, where it articulates directly with the jugal {Rhyncocephalia, 

 Theropodus Dinosaurs, and Phytosaurs), unhesitatingly called the quadratojugal. 

 If, on the other hand, we assume this bone to be a new element and the bone anterior 

 to it, in Pelycosaurs and Cotylosaurs, to be the quadratojugal, the skulls are radically 

 different from the Stegocephalian skulls, having one more element on the posterior 

 surface of the skull and one less in the temporal region. 



The condition of the Pelycosaurian skull gives a hint as to the condition of the 

 skull of Sphenodon. Baur claimed that in Sphenodon the squamosal and prosqua- 

 mosal had united in a single element, but Swinnerton and Howse found no trace 

 of any division of this element in even the youngest embryos. Is it not just as 

 probable that the prosquamosal dropped down to the lower edge of the skull and 

 formed the connecting link between the jugal and quadratojugal as that it rose 

 and fused with the squamosal ? In Paleohatierta the jugal joins the quadrate 

 direct,* but the squamosal (prosquamosal ?) projects down nearly between them. 

 The quadratojugal, if present, was on the back of the skull. 



As the Cotylosauria can no longer be considered as the primitive reptilian 

 type, and as the Rhyncocephalia can no longer be considered as derived from them 

 by the simple development of openings, the necessity of finding a prosquamosal 

 bone in the skull of the Rhyncocephalia has passed. 



The more definitely the anatomy of the primitive reptiles is known, the more 

 apparent it becomes that the theory which places the 

 Rhyncocephalia as a central type directly derived from 

 the Cotylosauria and giving rise to two main branches 

 of Reptilia is inadequate and must undergo a serious 

 re-examination. 



The maxillary does not have a great vertical ex- 

 tent, in any place, and beneath the orbit it is very slen- 

 der. Thirteen bluntly conical teeth may be counted 

 in the outer row, of which the fourth is the largest. 

 Just posterior to the enlarged tooth the alveolar edge 

 widens and there are three rows of irregularly placed 

 teeth, the inner is the shorter and the outer the longer, 

 so arranged that the whole patch is slightly crescent- 

 shaped. These teeth are frequently so worn that they Fir - 4' —Lower view of skull lof c. >«/«- 



r n . i i Li mus - x I- No. 4358 Am.Mus. 



appear as Hat-topped pegs rather than as blunt cones. 



The septom axillary bones (turbinate bones of Cope) are small elements appear- 

 ing at the surface in the lower inner corner of the nares. 



The lower surface of the skull: The prevomers are long and slender, meeting 

 in the median line and inclosing anteriorly the posterior ends of the premaxillaries; 



* Credner, Zeitsch. deutsch. geol. Gesell. Jahrg. 1888, 3, 546. 



