No. 2300. 



SKELETON OF DIMETRODON GIGAS—GILMORE 



529 



dition found to prevail in four other individuals in this same collection. 

 All authorities, I think, are now agreed that this part of the occiput 

 consists of a median supraoccipital, small exoccipitals, large para- 

 occipitals (opisthotics), and basioccipital. In addition to these 

 Huene in 1913 ^ recognized a distinct dermosupraoccipital (post- 

 parietal) bone lying between the upper extremity of the supraoccipital 

 and the parietal, and laterally a tabulare and supratemporal bones. 

 In assembling the bones of the present skull all of those preserved 

 could be articulated except the one illustrated in figure 2. It was 

 submitted to Dr. S. W. Williston, who identified it as being a portion 

 of the tabulare and dermosupraoccipital, but I have not been able to 

 satisfactorily articulate these bones, so they have been left ofl" the 

 skuU until such 



time as their 

 proper place shall 

 be definitely deter- 

 mined. 



The squamosal 

 shows on its medial 

 side a convex tri- 

 angular articular 

 facet (see fig. 1, 

 ta), which I first 

 regarded as the 

 surface for articu- 

 lation with the 

 concave area of 

 the so-caUed tab- 

 ulare shown in B, 

 figure 2. These 

 two surfaces seem 

 to be counterparts, 

 but unfortunately the tabulare appears to belong to the right side, 

 while the one squamosal present pertains to the left side of the skull, 

 so that a direct trial could not be made. Furthermore, I have never 

 been able to orientate the bones shown in figure 2, so that their relation- 

 ships with the other elements of the posterior aspect would be entirely 

 in harmony. Another suggestion as to the use of this articular facet 

 on the squamosal, arrived at since the skull was articulated, is that 

 it may be for the paraoccipital process. In the event of that fact 

 being estabUshed it would necessitate the shifting upward of the 

 whole central mass of the occiput to a higher position. Such a change 

 would bring the supraoccipital in contact on the ventral side with the 



Fig. 2.— Dimeteodon giqas occipital bones No. 8635, U.S.N.M. 



JNATUEAL SIZE. A, EXTERNAL ASPECT, d, DEKMOSITPBA OCCIPITAL; (., 

 TABULARE. B, INTERNAL ASPECT OF CONCAVE AKTICI7LAE SURFACE 

 OF TABULARE. 



« Bull. Amer. Mus. Nat. Hist., vol. 32, 1913, p. 359, fig. 44. 

 115690— 19— Proc.N.M.vol. 56 34 



