HISTORY OF THE CARNIVORA 575 



nychidae, the upper teeth underwent comparatively little change, 

 while the lower ones lost the inner cusps, but no carnassials 

 were formed. The face and jaws were elongated and the limbs 

 and feet became adapted to cursorial habits, and the more ad- 

 vanced genera had four-toed, completely digitigrade feet, with 

 blunt, almost hoof-like claws. A second series, the fArctocy- 

 onidse, likewise failed to develop sectorial teeth, the molars 

 becoming quadritubercular, with many accessory tubercles, 

 and assuming a bear-like or pig-like pattern, while the premolars 

 were reduced in size. The pentadactyl feet had sharp claws. 



In the fOxysenidse two pairs of carnassial teeth were 

 formed, of which the larger and more effective pair were the 

 first upper and second lower molar, the smaller pair the fourth 

 upper premolar and first lower molar. The teeth were dimin- 

 ished in number, first by the loss of the last molar, then the 

 suppression of the first premolar and finally by that of the third 

 incisor and second upper molar ; the remaining teeth were en- 

 larged. The upper carnassial molar (the first) was formed by 

 the approximation and partial fusion of the two external cusps 

 and the addition of a trenchant ridge behind these, and by the 

 reduction and eventual loss of the internal cusp, thus becoming 

 more exclusively shearing in function. The second lower 

 molar also lost the inner cusp and the heel, becoming remark- 

 ably cat-like in form ; the first was similar, but less simplified. 

 The face and jaws were greatly shortened, which, with the 

 widely expanded zygomatic arches, gave the head a very cat- 

 like appearance. The body and tail were long, the limbs short 

 and thick, and the feet had spreading toes and blunt claws. 

 Save for a notable increase in size and muscular power, the 

 foxyaenids showed but little change within the family. 



The fHyaenodontidse differed from the foxysenids in the 

 retention of all or nearly all the teeth and in having three pairs 

 of sectorials, of which the largest pair was the second upper and 

 third lower molar, but resembled them in the mode of forming 

 these sectorials and in the cat-like form of the inferior ones. 



