QUADRUPEDS. 165 



There is usually an obvious difference between the two 

 sexes. The neck of the male is thicker, his voice louder, 

 his size and strength greater than in the female. 



The more recent examinations of the Marsupial and Mo- 

 notrematous tribes, render the more common divisions of 

 quadrupeds insufficient for the purposes of systematical clas- 

 sification. The term Mammalia may still be the appella- 

 tive of those quadrupeds which suckle their young ; but it 

 must necessarily exclude the Monotremata, the young of 

 which, like those of birds, are either left to shift for them- 

 selves, or are guided by the mother to suitable food. 



MAMMALIA. 



Char. — The young, after birth, suckled by the mother. 



Descr. — The female is furnished with teats, and the 

 mouth of the young is fitted for sucking. There is an ute- 

 rus for the perfection of the foetus. The" external orifice of 

 the seminal canal is single. 



It appears to be necessary, in this place, to take notice, 

 more particularly, of the Teeth, as the characters furnished 

 by these organs, are extensively employed in the classifica- 

 tion of the mammalia. 



1. Structure of the Teeth. — The grinding surface of a 

 tooth is termed its Crown, or summit ; the portion which is 

 concealed by the gum its Root, or Fang ; and the interven- 

 ing part, its Body. These three parts are seldom construct- 

 ed of the same materials, but are usually formed from the 

 different substances which are termed Ivory, Enamel, and 

 Cement. 



The Ivory is harder than common bone, of a denser tex- 

 ture, and contains less animal matter. It bcems to consist 



