438 Bulletin American Museum of Natural History. [\o]. XX^"II, 



The Femur, Tibia and Fibula. 



The ancestral femur (p. 118) probably had a flattened expanded proximal 

 end, with greater and lesser trochanters forming a continuous ridge, between 

 which lay the sessile head. The femur was probably pointed outward, as 

 in Monotremes (p. 154), the patellar trochlea was flat, the third trochanter 

 not differentiated from the second trochanter ridge. The tibia was much as 

 in Monotremes, the fibula ended proximally in a wide expansion (cf. Mono- 

 tremes, Marsupials, Microgale). The pes was very likely turned partly 

 outward, the first digit being antero-internal (of. p. 435). 



Evolution of the manus and pes. 



The very important researches of Broom (1904.1) on the structure of the 

 feet in the Permian and Triassic mammal-like re])tiles and of Emery (1901) 

 on the embryonic manus and pes of Echidna and Didelphis, when com])ared 

 with the descriptions of the feet of Eocene mammals by Cope, Osborn, 

 Matthew and others and also with the feet in all the existing unguiculate and 

 ungulate orders, together furnish a fairly adequate basis for a review of the 

 evolution of the carpus and tarsus in mammals. 



Ill order to make clear what follows, the valuable figures given by 

 Broom and Emery are here brought together and arranged in such a manner 

 that they all now represent s])ecimens from the same side. 



A. The Carpus. 



Permian Amphibians and Therapsidans. — The prototypal form of the 

 mammalian carpus is more or less completely realized (Fig. 28, 2-4-) in 

 the carpus of the Permian Anomodonts Opisthoctenodon and Oiidenodon 

 and the lower Triassic Dromasaurian Galechirus, as figured by Broom. This 

 type is readily derived in turn from the still more generalized one realized 

 in the Permian Stegocephalian 7vnyo/j.v (no. 1). The orders to which these 

 genera belong are certainly much nearer to the ancestral mammals than is 

 the Water Tortoise (CheJ;/dra serpentina), the manus of which was selected 

 by Gegenbaur (cf. Flower, 1885, p. 281) as being prototypal to that of 

 mammals. Perhaps the most noticeable feature of the manus of Eryops is 

 its more or less fin-like, or paddle-like, character, but it shows practically 

 no feature in common with the largely hypothetical "cheiropterygium" and 

 " archipterygium " of Gegenbaur (1895), and it cannot be compared with 

 the paired fins of any known Devonian Dipnoans or Crossopterygians. It 



