On the Osteology of the Hyopotamidse. 177 



once placed among the Suina, and pronounced tetradactyle, though 

 the confluent tibia and fibula (mentioned by Leidy) might have been 

 taken as a warning against rash conclusions. I have found in the 

 cabinet of M. Aymard, in Puy, some bones of this animal ; few, 

 it must be acknowledged, but still leaving no doubt as to the di- 

 dactylism of Entelodon. Of this I shall try to adduce more extensive 

 proofs in a forthcoming memoir on this genus. How can the pre- 

 sence of a hog with such reduced limbs be explained in such ancient 

 deposits, when even the living Suidce have not yet reached this stage 

 of reduction ? The fact, however, is intelligible when we consider 

 that the Entelodon is the final result of the inadaptive development 

 and reduction along the line of tubercular-toothed Paridigitata ; it 

 is the culmination point of this group, and in this sense quite parallel 

 to the Anoplotherium in the other group. Thus the Paridigitata, 

 which split dichotomously in the earliest Eocene (?) into two groups, 

 the tubercular-toothed (Bunodonta) and the crescent-toothed (Sele- 

 nodonta), following the inadaptive mode of reduction, reached their 

 culmination-point in the Upper Eocene or just above it, in such 

 forms as Entelodon. for the first group, and Anoplotherium, Xiphodon, 

 Hyopotamus for the second group, which all became extinct with- 

 out any direct posterity. The living Suina and Euminantia are not 

 directly connected with them, but are the issue of lateral branches 

 which followed the adaptive mode of development and reduction. 



We may now consider the results of the adaptive mode of reduc- 

 tion. As I said before, the rate of this reduction is much slower 

 in the tubercular-toothed Paridigitata, or Suina ; and this gives us 

 the means of following more closely all the stages of reduction. 

 I propose, therefore, in the first place, to consider these. 



Though the published materials, as far as the skeleton is con- 

 cerned, are very poor, we have the means of giving nearly all the 

 intermediate stages between those genera in which the manus and 

 pes are conformable to the true tetradactyle type, every digit (except 

 the fourth and fifth, which are always borne by one) being carried 

 by a separate carpal and tarsal bone, and those in which the en- 

 tire distal surface of the carpus or tarsus is taken by the enlarged 

 two middle digits. 



The adaptation of these two middle digits on the adaptive line 

 forms a striking contrast to their rigidity exhibited by the other 

 mode of reduction ; and we shall briefly indicate the stages by 

 which the typical Suilline foot actually passed to reach the stage 

 exhibited now by Dicotyles. 



We are at a total loss to indicate the precise time when the 

 adaptive branch separated from the inadaptive ; it was certainly 

 somewhere in the lowest Miocene, as in the Middle Miocene we 

 find already a large quantity of Suina? in which the adaptive re- 

 duction has fairly set in. As the first stage I must consider a small 

 Suilline animal, though not the oldest, but perhaps a remnant of 

 the older type ; this is the Choerotherium, Lart., from Sansans. 

 The primitiveness of this small pig is indicated by the fact that 

 the carpal and tarsal bones retain their typical relation to the four 



Ann. & May. N. Hist. Ser.4. Vol xii. 12 



