MAMMALIA, 



527 



The skull of the dog has a dental formula of f yf f , and 

 it has thus two molars (one on each side) short of the full 

 typical Eutherian dentition. Jn this and in many other 

 respects the dog is the more generalised type of the two 

 \cf. diet). 



The cat has a dentition of f yf y, hence there has been 

 a great reduction in the number of teeth, especially as the 

 upper molar is also merely a vestige. In this case, how^ever, 

 as in the dog, the last premolar of the upper jaw and first 



364.— Ventral View of Lion's Skull x 



Note the large round tympanic bulla;, the wide zygomatic arch, the shortened 

 facial region and small number of cheek-teeth. Dental formula — 3.1.3.1. 



molar of the low^er jaw^ are the carnassial, hence it is easy to 

 observe which teeth have disappeared. Correlated w4th the 

 reduction in number of the teeth is the shortening up of the 

 jaws, involving a still further reduction of the facial region. 

 If the mandible be regarded as a lever (of the third order), 

 the " weight " will act at the level of the canines, the fulcrum 

 is at the glenoid cavity and the "power" at the insertion of 

 the jaw-muscles, a little in front of the glenoid cavity. 

 Hence the simplest w^ay of increasing the *' power" is to 

 move the *Sveight" nearer the ''fulcrum," or, in other 



