120 PRIMITIVE ANIMALS 



containing carbohydrate, fat, proteid and salts in 

 requisite proportion. 



As suckling proceeds the young Mammal begins 

 to prepare itself for a different kind of food, and it 

 begins to cut its first or milk-teeth. We have already 

 stated that the mammalian teeth are differentiated 

 into incisors in front, a pair of canines at the side, 

 and behind these a certain number of premolars and 

 molars. Of these teeth only the incisors, canines 

 and premolars are represented by milk-teeth, which 

 are replaced by permanent teeth afterwards ; the 

 molars or grinders are not developed as milk-teeth 

 which are subsequently replaced, but they appear for 

 the first time as permanent teeth synchronously with 

 the appearance of the other permanent teeth in front. 



The reason why milk-teeth are developed by the 

 young Mammal is that, at the period when suckling 

 ceases and the animal has to masticate solid food, 

 the head and jaws have not attained by any means 

 to their full size and there would not be room either 

 for the full complement of teeth or for teeth of so 

 large a size as are required by the more powerful 

 adult animal. Hence the young Mammal is first of 

 all furnished with a set of small milk-teeth without 

 any molars at the back, w r hich are gradually replaced 

 as the head and jaws begin to attain their adult size, 

 the molars being added at the back of the jaws as 

 the last of the series. 



