ON THE STRUCTURE OF THE FORE FOOT OF 

 DIMETRODON. 



During the summer of 1903, while in charge of the University of 

 Chicago expedition in the Permian fossil fields of Texas, the author 

 collected the right fore leg and foot of a Pelycosaurian reptile of the 

 genus Dimetrodon. The species is not determinable at present, but 

 is very close to Dimetrodon incisivus, if not that species exactly. When 

 found the bones were badly softened by decay, but after cleaning 

 and hardening I find that those of the carpus, with one exception, are 

 perfectly preserved and in their natural positions. This is particu- 

 larly fortunate, as it is the exception to find any considerable portion 

 of a skeleton together in the Texas fields. 



The author has previously described^ an imperfect front foot of 

 Dimetrodon, No. 114 of the University of Chicago collection, and 

 attempted to place the bones in their natural relations. The present 

 specimen shows that the position of the bones in the figure was 

 erroneous and must be corrected. 



Fig. I shows the right front foot from the lower surface. The 

 bones added from another specimen are in line only. The specimen 

 has received the number 1003 in the University of Chicago collection 

 of vertebrate fossils. 



A study of the specimen brings out first of all the striking resem- 

 blance of the foot to the foot of Sphenodon (Fig. 2), not only in the 

 number of the bones, but in the arrangement and to some extent the 

 form. This emphasizes the Ryhnchocephalian nature of the Pely- 

 cosaurs already demonstrated from the structure of the skull. 



The carpus consists of eleven elements. The ulnare is a stout 

 bone with wide proximal end, and resembles the same bone in Sphen- 

 odon very closely. The radiale is larger than the ulnare, but is not 

 so stout; it is very thin, but elongate and articulates with the distal 

 row of carpals. The intermedium reaches well up between the radius 

 and ulna. There are two centrale. Centrale i occupies a central 



I Journal of Geology, Vol. XI, No. i (1903), p. 11. 



312 



