314 



E. C. CASE 



Fig. 2. — Upper side 

 left manus of Spheno- 

 doii after Bayer and 

 Howse, from Osborn. 

 Lettering as in Fig. i . 

 Natural size. 



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 1 001 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 

 S phenodon, 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. 

 The first digit was shorter and stouter than 

 the second. The broad proximal end is char- 

 acteristic of the first metacarpal. The second 

 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 fifth metacarpal is a very 

 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. In the description and figure of 

 114 they were called first and second. 



It is interesting to compare the carpus of Dimeirodon with the 

 carpus of Procolophon in the fight of Broom's determination of the 

 Rhynchoce phalian nature of Procolophon.^ Fig. 3 is an outline 



I Broom, Records of the Albany Museum, Vol. I, No. i (1903). See also Osborn, 

 Memoirs 0} the American Museum of Natural History, Vol. I, No. 8 (1903), p. 480. 



Fig. 3. — 'NLarms oi Procolophoji. 

 From Osborn after Broom. 

 Lettering as in Fig. i. Natural 

 size. 



