COMPARATIVE ANATOMY OF THE TEETH. 2*73 



to side, while in the rodentia they are antero-posterior, 

 showing the friction to be from front to back. 



In the carnivora, on the other hand, or those that live on 

 flesh, there is very little wearing away of the teeth, scarcely 

 any lines from friction to be seen, and the points and cut- 

 ting edges are preserved to the end of life. This ine- 

 quality in the wearing of the teeth has been turned to 

 practical account in determining the age of the horse, and 

 the incisors are those by which the age is known. " The 

 middle teeth, says M. Cuvier, begin to appear about fifteen 

 days after birth, and at two years and a half the middle 

 ones are replaced ; at three and a half the two next follow, 

 and at four and a half the outermost or corner teeth. All 

 these teeth with originally indented crowns, lose by degrees 

 this character by detrition. At seven and a half or eight 

 years the depressions are completely effaced, and the horse 

 is no longer marked. The inferior canines appear at three 

 years and a half, the superior at four years. They remain 

 pointed until the sixth, and at ten begin to peel away." 

 The horse seldom lives longer than thirty years. 



With these general remarks, we will now proceed to run 

 a very brief contrast between the teeth of the different or- 

 ders of the class mammalia and those of man, commencing 



/ o 



with the highest in the scale and then descending. The 

 first order is the 



QUADRUMANA. This order is divided into the monkeys, 

 simicB) and lemurs. The chimpanzee and ourang-outang con- 

 stitute the highest order of monkey, and are next to man 

 in their organization. According to Mr, Owen, the most 

 prominent points of distinction between the dentition of 

 man and that of these higher quadrumana, consist in the 

 " absence of the interval between the upper lateral incisor 

 and the canine in man, and the comparatively small size 

 of the latter tooth," (Fig, 75.) 



The human teeth are more equal in size, and describe a 

 more regular curve in both jaws, and do not, as just 

 stated, present the vacant space of the monkey. The in- 

 cisors of the human teeth are smaller in proportion to the 

 18 



