Paleontology. 185 



belonged to a very early mammal, antecedent to the 

 elephant series, the horse series, the rhinoceros, the 

 hog, and, in short, all the known hoofed mammalia 

 (Fig. 80). It was presumably an inhabitant of 

 swampy ground, slow in its movements, and low in 

 its intelligence. 



But now, as we have seen, for more rapid progression 

 on hard uneven ground, a stronger and better jointed 

 foot would be needed. Therefore we find the bones 

 of the wrist and ankle beginning to interlock, both 

 among themselves and also with those of the foot and 

 hand immediately below them. Such a stage of 

 evolution is still apparent in the now existing elephant. 

 (See Fig. 81.) 



Next, however, a still stronger foot was made by 

 the still further interlocking of the wrist and ankle 

 bones, so that both the first and second rows of them 

 were thus fitted into each other, as well as into the 

 bones of the hand and foot beneath. This further 

 modification is clearly traceable in some of the earlier 

 perissodactyls, and occurs in the majority at the 

 present time. Compare, for example, the greater in- 

 terlocking and consolidation of these small bones in the 

 Rhinoceros as contrasted with the Elephant (Fig. 81). 

 Moreover, simultaneously with these consolidating im- 

 provements in the mechanism of the wrist and ankle 

 joints, or possibly at a somewhat later period, a reduc- 

 tion in the number of digits began to take place. This 

 was a continuation of the policy of consolidating the 

 foot, analogous to the dropping out of the sixth row 

 of small bones in the paddle of Baptanodon. (Fig. 

 78.) In the pentadactyl plantigrade foot of the early 

 mammals, the first digit, being the shortest, was tiu 



