GREGORY, QUADRUPEDAL LOCOMOTION 285 



reverse is the case, is shown by the table of ratios, Plate XXXIV, and 

 especially in the following examples: 



„ . Length of metatarsal III 

 ' Length of femur 



Grariportal Mediportal Subcursorial Cursorial 



Coryphodon.. . .14 Rhinoceros .37 Eohippus . . . .50 Equus 78 



Uintatherium . .10 Palseosyops .21 Tragulus 56 Antilope. . . . 1.00 



Mastodon 11 Mesohippus. .57 Odocoileus . . 1.00 



Elephas 13 



Brontotherium .20 

 Toxodon 17 



These ratios definitely prove the connection between the mode of loco- 

 motion and the length of the middle metatarsal as compared with the 

 femur. The wide differences in the metatarso-femoral ratio, ranging 

 from .10 in extreme graviportal forms to 1.00 and upward in cursorial 

 forms, are partly bridged over in the mediportal and subcursorial types, 

 and even more completely in a fifth group including certain primitive 



Mts. III. 



ungulates, the Condylarths, in which ranges from .43 to .31. 



F. 



Perhaps the most important facts to keep in mind in comparing these 

 and similar ratios (below) are that the ancestral Placentals probably 

 had relatively short hands and feet and long limb bones (p. 270), but 

 that there was doubtless a considerable range of variation in this respect 

 even as far back as the Upper Cretaceous epoch. We are unfortunately 

 unable to follow the ratios through approximate phyletic series except 

 in a few cases (especially Titanotheres, Equidse, Khinocerotidae), but, in 

 every case, we can feel sure that the precise ratios attained in the end- 

 forms are conditioned largely by the nature of the ratios in the stem- 

 forms of each family. 



Thus, the exceptional shortness of the feet in the Amblypoda is con- 

 ditioned by the fact that this group, as represented by Pantolambda, had 

 comparatively short feet before gigantism was developed. Hyrax is 

 another example of a small form with very short feet, and from some 

 such forms the Proboscidea probably arose. 



Besides those phyla which had short feet in the ancestral forms and 

 which merely emphasized this feature, there are many phyla which 

 started from animals with feet of moderate length and later shortened 

 up the feet to a considerable extent. Thus in the Titanotheres, the oldest 

 and most primitive form (Eotitanops) has a metatarso-femoral ratio of 

 about .34, which is not far from that of other early Perissodactyls, but 



