HISTORY OF THE CARNIVORA 519 



nassial" teeth, always the fourth upper premolar and first 

 lower molar, which form a pair of shearing blades, the pre- 

 molar biting outside. In the bears and most of the raccoons 

 the teeth are tuberculated, in adaptation to the omnivorous 

 habit, and the carnassials have lost the shearing form, though 

 clearly derived from that type. The skull has powerful jaws, 

 and the crests and ridges for the attachment of the jaw muscles 

 are prominent except in very small animals, and the stout, 

 boldly outcurving zygomatic arches are very characteristic. 

 The face may be elongate, as in the dogs, or extremely short, 

 as in the cats, or of intermediate length ; the brain-case is 

 relatively capacious, and the orbits, except in 'the cats, are 

 widely open behind. The neck is never very long, but the 

 body often is, and the tail varies greatly in length, as do also 

 the limbs. There is great difference, too, between the va- 

 rious families in the prominence of the processes on the limb- 

 bones for the attachment of muscles, as expressive of the mus- 

 cular development of the limbs, and also in the extent to which 

 the fore foot can be rotated and used for grasping. In all exist- 

 ing Fissipedia the femur has no third trochanter, but many 

 extinct genera possessed it. The bones of the fore-arm and 

 lower leg are always separate and uninterrupted. 



In the wrist (carpus) there is always a large bone, the scapho- 

 lunar, which is made up by the coalescence of three elements, 

 the scaphoid, lunar and central, a feature which, though recur- 

 ring in a few other mammals, is essentially characteristic of 

 the modern Carnivora. The feet are armed with claws more 

 or less sharp, which in some families, notably the cats, are 

 retractile and may be folded back into the foot. The gait 

 may be plantigrade, as in the raccoons and bears, or digiti- 

 grade, as in the dogs and cats, or intermediate in character. 



Throughout the Paleocene and most of the Eocene, there 

 were no Fissipedia, the flesh-eaters all belonging to the extinct 

 fCreodonta, and the first clearly recognizable fissipedes occurred 

 in the upper Eocene or Uinta. 



