Sea ore te S 
1884.] The Creodonta. 345 
flat, with only a very slight median ridge for the groove of the 
astragalus. e internal malleolus is very large. 
“The astragalus is but slightly concave from side to side, much 
less So than in Mesonyx. 
“The foot is plantigrade, and the entire length of the calcan- 
eum rested on the ground. Five well-developed digits were pres- 
ent, terminating in short and stout compressed claws; very differ- 
ent from the peculiar depressed ungual phalanges of Mesonyx ; 
otherwise the resemblance of the foot as a whole to that of Meso- 
nyx is very striking. 
“The brain case attributed by Gervais to Hyzenodon must be- 
long to some other genus, or else our American species differ very 
radically from the French. In the American species the brain is 
relatively very small and simple, being but slightly larger than 
that of Thylacynus, to which animal Hyznodon presents man 
interesting approximations in the structure of the skull and teeth. 
The cerebellum of Hyzenodon is entirely uncovered by the hemi- 
spheres, which in their turn seem to have but three straight longi- 
Mais ee gyri, presenting the simplest type of the carnivorous 
rain.” 
It is highly probable that this family is a derivative of a 
pentadactyl form of the Mesonychidæ. Its appearance in time 
corresponds nearly with the disappearance of the latter. 
But one genus of this family has been thus far described, the 
Hyænodon of Laizer and Parieu. Its dental formula is I. 3; C. 
1; P-m.{; M. 3. The last three molars in both jaws are sectorials, 
and the last of these are the largest, and form the most effective 
Shears for the dividing of animal tissues. The position of these 
teeth indicates a mouth fissured far posteriorly, and a correspond- 
ingly posterior position of the masseter muscle. This structure 
indicates a weak power of prehension of the canine teeth. This 
5 er is sustained by the frequently anteriorly directed infe- 
"or canines, and the generally slender mandibular rami. The 
Hy ænodons must be regarded as snappers, and not capable of 
holding on to a living enemy with much persistency.’ They were 
evidently weaker in all points of organism than the modern Car- 
nora, which no doubt accounts for their extinction. Thirteen 
YAp have been described, all but three North American forms 
being French. The oldest of these, the H. parisiensis Kefst., is 
ite the Upper Eocene or Oligocene, or the Paris Gypsum, but 
Teference to this genus is not yet certain. Gaudry, however, 
ede the origin of the sectorial tooth of the Carnivora, AMERICAN NATURAL~ 
3 1970, P. 17. 
