74 Vertebrata. 



on the advent of cold weather, about the first week of 

 October. 



CHAPTER XIV. 



CLASS 5, MAMMALIA. 



49. General Characters. This, the highest class 

 of vertebrate animals, includes all those viviparous, 

 warm-blooded animals which are provided with super- 

 ficial dermal glands for the purpose of secreting a 

 fluid called milk for the nutrition of the young until 

 they are able to seek out other nutriment for them- 

 selves. They are for the most part terrestrial in habit ; 

 they are all provided with epidermal covering in the 

 form of hairs ; and the lower jaw in them articulates 

 directly with the base of the skull, the quadrate bone 

 being very small and included in the ear cavity, so 

 that it is of use only in conveying sound-waves to the 

 nerves of hearing. Man, all quadrupeds, seals, whales, 

 and bats are examples of this class. 



The superficial clothing of hairs characteristic of 

 the class may be only transitory, as in whales and 

 some thick-skinned animals, or the hairs may be 

 thick and spine-like, as in the porcupine and hedge- 

 hog, or they may be united into scales, as in the 

 manis and armadillo, or on the tail of a rat. Each 

 hair is the epidermal secretion of a single papilla, and 

 is a solid cylinder composed of long cortical or super- 

 ficial cells, and rounder central cells. The hairs arise 



