1873.] 



Osteology of the Hyopotamidse. 



159 



sequence of this, the distal surface of the carpus was much broader than 

 the proximal surface of the two functional digits — an arrangement not 

 calculated for firm equilibrium. Now the confluence of the two middle 

 digits is always followed by a considerable contraction ; and if this 

 coalescence should occur in the imperfectly adapted foot of Anoplotherium, 

 and especially XipJwdon, all equilibrium would be lost. If ever such conflu- 

 ence occurred, by reason of the tendency to the greatest possible reduction, 

 the resulting form had not the least chance of being propagated and of hold- 

 ing its ground against the competing genera. The broadening of the middle 

 digits could not occur after the entire loss of the laterals ; and we shall see 

 that, in genera which have left immediate successors (Sus, Hyomosclius), 

 the lateral digits are not allowed to go until the middle ones have obtained 

 a secure footing on the entire distal surface of the carpus and tarsus. 

 However, these inadaptively reduced genera of the Eocene could perhaps 

 have lived till our own days ; but the development of the competing and 

 better adapted forms pressing them on all sides, they had no chance to 

 stand their ground against them, and became extinct without any direct 

 posterity, while the succession of the Paridigitata Selenodonta was carried 

 by a side branch, and reached its culminating point in the Miocene, 

 continuing from thence to our own days. 



"We turn now to the same mode of inadcvptive reduction as manifested by 

 the tubercular-toothed Paridigitata (Bunodonta), or Suina. The old repre- 

 sentatives of this group are very little known. The Choerojpotamus is a 

 very doubtful genus, and may be inclining towards the crescentic-toothed 

 Paridigitata, being supposed to be the progenitor of the Antliracotfieridce 

 and Hyopotamidce. Besides it we have the Acotlierulum saturninum, Ger., a 

 truly tubercular-toothed Paridigitate from the Upper Eocene, Acotlierulum 

 Campichii (Dichdbune, Camp. Pictet) from the Lower Eocene of Mauremont, 

 and a larger pig-like animal from the same deposit not yet described or 

 named. These are undoubtedly the oldest tubercular-toothed Paridigitates 

 we know; but unfortunately our knowledge is based only on dental 

 characters. However, considering that even the recent Suina have not 

 yet completely lost their two lateral digits, it may, with the greatest pro- 

 bability, be inferred that these old Eocene forms were tetradactyle. Our 

 knowledge of the development of this group is very incomplete ; but there 

 can be no doubt that, though not nearly so rich as the Selenodont group, 

 they were still numerous, as may be inferred from the great quantity of 

 the Suina in the Miocene, and such forms as the Listriodon sjplendens *. 

 We are so accustomed to look on the Suina as a group of tubercular- 

 toothed tetradactyle Paridigitata, that no one ever thought of the possibility 

 of a didactyle hog ; but, strange as it may seem, such a Suilline animal 



* I have not been so fortunate as to see any bones of the Listriodon ; but as this 

 miocene hog died without any successors, T should not be astonished if it proves to be 

 didactyle, thus being a parallel to Hyopotamus in the same sense as Entelodon is 

 parallel to Anojplot her turn. 



