MORPHOLOGICAL REVISION OF THE SUBORDER. 83 



The condition of the arches is very uncertain. In Diiiietrodoii there are two 

 bones, the quadra to-jugal and prosquamosal overlj'ing the posterior edge of the quad- 

 rate and the upper temporal vacuity is greatly reduced in size. In this specimen 

 there is a single bone overlapping the posterior edge of the quadrate and extending 

 forward to join the jugal (plate 3, figs, i and 4). This occupies the position of both 

 the quadrate and prosquamosal in Dimetrodon. A very careful search fails to reveal 

 any suture that would indicate a division of the bone; there are several cracks in the 

 position of such a hypothetical suture, but they do not appear to be other than acci- 

 dental breaks. As the anterior end of this bone without doubt joined the jugal it 

 occupies the position of the prosquamosal in Dimetrodon^ but as its posterior portion 

 overlaps the posterior edge of the quadrate it occupies the position of the quadrato- 

 jugal. It is hardly supposable that the two bones are united, however, for the animal 

 is undeniably far more primitive than Dimetrodon and the two bones should be 

 separate. There is the possibility that the quadrato-jugal was a thin, scale-like bone, 

 as indicated by its form in Dimetrodon^ and has been lost, but the condition of the 

 bones gives little warrant for the assumption. The upper edge of the anterior portion 

 formed the lower edge of a large inferior temporal vacuity. 



Above is a second bone, occupying the position of the squamosal in Sphenodon 

 and with a similar form. The upper end is divided into two parts ; the lower extends 

 forward, but its anterior end is broken and the connection can not be made out. The 

 upper and lower edges of this process are thin and show that they formed the edges 

 of the upper and lower temporal vacuities. According to this process the upper 

 vacuity was as large as the lower. The upper end of the bone has a distinct face 

 probably for the parietal bone. 



Some light seems to be thrown on the condition of the temporal region by the 

 specimen of Vaj'aiiosaiiriis. It resembles the other Poliosauridcc in so many respects 

 that it may safely be assumed that it was similar in the temporal region as well. The 

 postorbital region of Varanosaiirus is preserved, but not the articular region ; there 

 was a great superior temporal vacuity and probably an inferior one as well. Broili 

 speaking of this region in correspondence says : "Ich kann jederseits riickwarts der 

 Augenhohlen je eine Offnung constatiren. Da die riickwartige Begrenzung derselben 

 fehlt, ist es immerhin noch moglich und sogar wahrscheinlich, dass noch eine ate 

 Offnung vorhanden war; wurde aber dann nicht wie bei Dimetrodon oben sondern 

 an den Flanken des Schadels liegen." 



It seems probable that the members of this more primitive family had two wide 

 temporal vacuities. If this be true, then the small superior temporal vacuity of the 

 long-spined forms is an additional evidence of the extreme specialization of the order. 



On the lower surface of skull the basisphenoid and the pterygoids are preserved. 



The stapes is a slender rod of bone with an expanded proximal end. The shaft 

 is slender and was quite elongate, but only the proximal portion is preserved. The 

 proximal end is divided into two unequal parts by a very deep groove. Just distal to 

 this groove the shaft is perforated by a foramen, which passes through somewhat 

 obliquely. This bone was regarded by Baur and Case as a possible rib (9), but this 

 seems to haVe been an error ; the finding of the elongate portion of the stapes in posi- 

 tion in the skull of Dimetrodon gigas and the proximal end of a stapes with its per- 

 foration in Edaphosaurns pogonias show that Cope was correct in his determination. 

 The form of the bone is shown in fig. 22. Cope compared this element directly with 

 the stapes of the Monotreme Mammalia and considered that its discover}' strengthened 

 considerably his idea that the Pelycosaiiria were the ancestors of the mammals. 



