12 MAMMALS. 



jWammalia. 



(The Mammals.) 



A Mammal is a warm-blooded, air-breathing vertebrate, 

 having the skin more or less covered with hair; vivipar- 

 ous; embryo developed from a minute egg, and provided 

 with an amnion and allantois; young nourished for a 

 time after birth by milk, secreted in the mammary 

 glands of the mother; respiration never by branchia 1 , 

 but after birth by lungs, suspended freely in the thoracic 

 cavity, which is completely separated from the abdominal 

 cavity by a muscular septum (the diaphragm); heart 

 with four cavities; a complete double circulation. The 

 peculiarities of the skeleton are too numerous to be 

 noticed in this connection. 



The following key to the Orders and Families of 

 Mammals which occur within our limits (omitting the 

 Seals and the Cetaceans, all our members of which 

 groups are marine), is mostly taken from Prof. Gill's 

 "Arrangement of the Families of Mammals." It has 

 been thought best not to give here any separate account 

 of the different orders, as, in the abundance of literature 

 on that subject, it seems unnecessary. 



ORDERS OF MAMMALIA. 



* Young not born until of considerable size and nearly perfect 

 development, deriving its nourishment, before birth, from 

 the mother through the intervention of a placenta; a well 

 developed corpus callosum. (MONODELPHIA.) 



f Brain with a relatively large cerebrum, overlapping much, or 

 all, of the cerebellum and olfactory lobes. (EDUCABILIA.) 



