682 CARNIVORES xxvn. 4- 



seals, the teeth most favourably placed for biting by their position 

 relative to the jaw muscles, namely, the last upper premolar and first 

 lower molar are specially developed into cutting-blades, the carnas- 

 sials. This is done by formation of a ridge along the outer side of the 

 upper molar, the paracone and metacone making a single cutting- 

 edge. The protocone remains as an inwardly projecting ridge at the 

 front of the tooth, which otherwise makes a single blade, shearing 

 outside a similar blade formed by the paraconid and protoconid of 

 the lower molar. This restriction to long sharp ridges also affects the 

 teeth in front of the carnassials, but behind them the molars are so 

 reduced that in true cats they are represented only by a single vestige 

 in each jaw. More of the posterior molars remain in some of the 

 primitive carnivores (dogs), and in some, such as the bears, they may 

 acquire a bunodont surface and hence the power of grinding. 



The jaws are, of course, powerful in carnivores, the articulation 

 being a tight, transverse hinge, allowing none of the rotatory move- 

 ments found in other mammals. The jaw-muscles include especially 

 powerful temporals, for whose attachment there is a large coronoid 

 process on the jaw and often large sagittal crests on the top of the skull. 

 The temporal fossa is very wide and never closed off from the orbit, 

 since there is no need for specially increased surfaces for the masseter, 

 which is only moderately strong. The pterygoid muscles (and their 

 fossa) are reduced, since the jaw has no rotary action. 



The post-cranial skeleton shows a generalized mammalian build, 

 with specializations for sudden leaping movements. There are five 

 digits in the hand and four in the foot in cats; in other carnivores 

 the number is never less than four. The toes are armed with the 

 characteristic claws, which are held drawn back by elastic ligaments 

 and pulled out when needed by the action of the flexor digitorum 

 profundus muscles on the terminal phalanx, to which the claw is 

 attached. The weight of the body is carried on special pads on the 

 second interphalangeal joints and the metatarsal heads. A curious 

 feature of the carpus of all modern carnivores is the fusion of the 

 scaphoid and lunate bones. The arrangement of the limbs and back- 

 bone is that of a quadruped able to proceed over uneven surfaces and 

 also steeply upwards and downwards, especially in the carnivores that 

 are arboreal. This involves a long body, with much of the weight 

 carried on the fore-limbs; the thoracic neural spines are therefore 

 high. On the other hand, the vertebral girder has to take the strain of 

 powerful sacrospinalis muscles for leaping; the transverse processes 

 are broad in the lumbar region, and again in the neck for the muscles 



