44 



AMERICAN PERMIAN VERTEBRATES 



see no perforating foramen between the two bones. The distal 

 and inner facets are also very broad, subquadrate in outline, with 

 rounded angle. The fibulare is a larger bone, but much thinner 

 than the tibiale; its tibial side is the thickest. I identify these 

 two bones as the usual fused tibiale and intermedium, and the 

 fibulare, but it is not impossible that the tibiale has been entirely 

 lost, after fusion, and that what really remains are the intermedium 



and fibulare. I have so far found no 

 evidence satisfactory to me that the 

 tibiale and intermedium are ever pres- 

 ent in adult reptiles as distinct bones. 

 I am aware that Broom has provision- 

 ally recognized a separate intermedium 

 in Howesia, and that other instances 

 have been cited, but I think they are all 

 open to doubt. The separation of the 

 intermedium of the hand is a very per- 

 sistent character in the Amniota, man 

 himself even having the same bones that 

 are found in the temnospondyls in the 

 proximal row of the carpus. In the tar- 

 sus, however, there was an early speciali- 

 zation as far back as early Carbonifer- 

 ous times, and I do not think there was 

 ever a reversion to the amphibian type. 

 Of the left foot of specimen 908 only 

 these two tarsal bones and a number of 

 separated toe bones have been recovered. 

 Of the right foot, however, all the bones 

 of the toes were preserved in their natural relations in the matrix, 

 or with but slight distortions, the metatarsals all lying in one plane, 

 apparently quite in the positions they occupied in life. The block 

 containing them had the phalanges of the first toe, the first one of 

 the second toe, the first two of the third toe, and all four of the fifth 

 toe in close articulation, those of the first and fifth toes strongly 

 flexed. With this block, but separated, were the phalanges of the 

 middle toes, the two each of the second and third and all five of 



Fig. 17. — Eosa annus copei 

 Williston. The oldest known 

 reptilian tarsus and foot . Mid- 

 dle Pennsylvanian. 



