556 LAND MAMMALS IN THE WESTERN HEMISPHERE 



capacity and the face varied much in length in the different 

 famihes. Primitively, the face and jaws were short in correla- 

 tion with the small size of the teeth, and this primitive con- 

 dition was modified in two opposite directions ; in one the 

 face and jaws were elongated, as the teeth enlarged, and in the 

 other they were shortened still further. The zygomatic arches 

 were stout and curved out strongly from the sides of the skull, 

 making very wide openings, and, in almost all cases, the sagittal 

 and occipital crests were very high, as would be necessary from 

 the combination of powerful jaws and small brain-case (see 

 p. 63). The tympanic bullae were not ossified. The brain 

 was extremely small, especially in the more ancient genera, and 

 the convolutions were almost always few and simple, which in- 

 dicates a low grade of intelligence and very marked inferiority 

 to the Fissipedia. 



In all the genera of which sufficient material has been ob- 

 tained the body was long and had 19 or 20 trunk- vertebrae : 

 in the lumbar and posterior part of the dorsal regions the pro- 

 cesses by which the successive vertebrae were articulated to- 

 gether (zygapophyses) were cylindrical and interlocking, as 

 in the artiodactyl ungulates (p. 360). To this general state- 

 ment, the fMiacidae formed a partial exception. The tail 

 was very long and heavy in all the forms of which the caudal 

 vertebrae are known, and this was probably true of all. The 

 limbs were short and generally heavy ; the femur had the 

 third trochanter and the humerus, save in a few of the later 

 genera, the epicondylar foramen, and the manus could, in 

 nearly all, be freely rotated. Except in the most advanced 

 forms of one family, the fMesonychidae, the feet were five- 

 toed and plantigrade, or semi-plantigrade, and of decidedly 

 primitive structure. The scapholunar bone of the Fissipedia 

 (see p. 519) was not formed, its three elements, with very few 

 exceptions, remaining separate. The astragalus nearly always 

 had a shallow groove, or none at all. The claws were thick and 

 blunt and the ungual phalanges cleft at the end, except in the 



