528 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 56. 



not raise his body far above the ground, but crawled around much 

 after the fashion of the crocodile, though, quoting again from the 

 above author: 



The strong limbs with longer foreleg than upper leg, with strong feet, with powerful 

 claws, ample evidence of an ability to run with some speed and perhaps even leap or 

 pounce upon prey. Abel, in hia Paleobiologie, points out that running and leaping 

 animals have the foreleg longer than the upper leg, and creeping animals have the pro- 

 portions reversed. It is not probable the Dimetrodon was ever capable of leaping any 

 distance, but it certainly was able to move swiftly for a short space. Probably it 

 lay hidden in the vegetation, and made short, scuttling rushes upon its prey, end- 

 ing, possibly, with a short 

 ■^ pounce, which permitted its 



-^a/ weight to add something to 



P- /^ j^is^^-^- ' JT'^^^^^:^'^^^^ v&o. *^® vigor of the attack by 



tooth and claw. 



Dimetrodon was the 

 dominant and prob- 

 ably the most formid- 

 able animal of his time. 

 Of the contemporary 

 animals of the Permian 

 there was a vast assem- 

 blage of reptiles and 

 amphibians, and it 



Fig. 1.— Dimetrodon gigas, posterior aspect of skull. No. WaS thcSC that the 

 8635 U.S.N.M. One-fourth natural size. K. frontal; o., j -^^ 1_ 



orbit; occ., occipital condyle; P., parietal; po., postorbital; . •• ^ 



P. oc., paraoccipital; po. /., postfrontal; q., quadrate; q. j., iarly adapted for catch- 



quadratojugal: So., supeaoccipital; Sq., squamosal; ta., -^^^ rji-i hnrripr<5 nf 



doubtful articulation for the tabulare. 



mg. 



pools and swampy 

 places were probably the regions most densely populated by these 

 lesser forms, and no doubt such places were the favorite haunts 

 of the Dimetrodon. 



NOTES ON THE SKELETAL STRUCTURE OF DIMETRODON GIGAS COPE 



STcuU. — Through the studies of Baur, Case, Williston, Broom, and 

 von Huene, the structure of the skull of Dimetrodon is now pretty 

 well known. There is still divergence of opinion regarding the extent 

 of the boundaries of some few of its elements, and of the homologies 

 of certain others. At this time it is the composition and extent of 

 the bones forming the posterior part of the cranium that appears to 

 be least understood, and while the skull of No. 8635, U.S.N.M., 

 ojffers but little positive information for making clearer our under- 

 standing of the occipital region, it does offer suggestions which may 

 eventually be of help in arriving at the correct interpretation of these 

 parts. 



The median bones of the occipital region were found articulated 

 as shown in figure 1. The sutures are entirely obliterated — a con- 



