THE FORE FOOT OF DIMETRODON 85 
this specimen were somewhat scattered, so that, although the bones 
of the fore legs and feet were preserved, they were not in position. 
From the specimen 1003 the bones of the carpus of both sides in speci- 
men roor have been placed in position, and both show the presence 
of an extra element which, from the position of 
articular surfaces and from comparison with 
Sphenodon, evidently occupies the position of the 
pisiform bone on the ulnar side of the mammalian 
carpus. It is a sesamoid bone of considerable 
size. 
The bones of the carpus fit snugly together, 
with well-developed articular surfaces, making a 
strong foot. ‘This is also shown by the possession 
of well-developed phalanges and powerful claws. 
Fic. 2.—Upperside 
left manus of Spheno- 
The first digit was shorter and stouter than 
don after Bayer and the second. The broad proximal end is char- 
Howse, from Osborn. acteristic of the first metacarpal. The second 
Lettering as in Fig. 1. 
Natural size. 
digit was probably the largest of the foot, judg- 
ing from the length of the metacarpal and the 
imperfect foot of specimen 114. The third and fourth metacarpals 
are more slender than the second. The 
broad and thin bone articulated to the 
prominent fifth carpal, so that it stood 
out from the others at a considerable angle. 
The articular surface between the fifth 
carpal and metacarpal is twisted in a 
peculiar manner, so that it permits of a 
considerable range of motion. This per- 
haps explains the fact that the fifth meta- 
carpal and digit were found in the speci- 
men 114 lying at right angles to the 
fourth. Jn the description and figure of 
114 they were called first and second. 
fifth metacarpal is a very 
Fic. 3—Manus of Procolophon. 
From Osborn after Broom. 
Lettering as in Fig.1. Natural 
size. 
It is interesting to compare the carpus of Dimetrodon with the 
carpus of Procolophon in the light of Broom’s determination of the 
Rhynchocephalian nature of Procolophon.t Fig. 3 is an outline 
t Broom, Records of the Albany Museum, Vol. 1, No. 1 (1903). See also OSBORN, 
Memoirs of the American Museum of Natural History, Vol. 1, No. 8 (1903), p. 480. 
