ON Ti STRUCTURE OF THE FORE FOOT OF 
DIMETRODON. 
Durtnc 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 Dimeirodon. ‘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 describedt 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. 1 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 S phen- 
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 1 occupies a central 
t JOURNAL OF GEOLOGY, Vol. XI, No. 1 (1903), p. II. 
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