68 CHARACTERS OF VERTEBRATE ANIMALS 



It is characteristic that the cerebral hemispheres should be 

 large, and united by a corpus callosum, while their surface is 

 usually marked by more or less distinct convolutions. There is a 

 relation between the intelligence of a Mammal and the size and 

 complexity as regards convolutions of its hemispheres. 



CLASSIFICATION OF MAMMALS 



Existing Mammals fall into three natural groups, which are 

 again subdivided into Orders, the arrangement being as follows : — 



A. EuTHERiA. — This group embraces the vast majority of 

 Mammals, including all the highest forms and those with which 

 we are most familiar in this country. The distinctive characters 

 mostly require a specialist knowledge of anatomy to be appreciated, 

 and it may suffice to state that the hemispheres of the brain are 

 large and convoluted, and that the young are born in a compara- 

 tively perfect condition, never being sheltered in a pouch after 

 birth, as is the case with the second group of Mammals. 



The orders are as follows: — 



1. Primates. — Exs.: Man, Apes, Monkeys. 



2. Lemurs (Lemuroidea). 



3. Bats (Chiroptera). 



4. Insect-eaters (Insectivora). — Exs.: Hedgehog, Mole, Shrew. 



5. Flesh-eaters (Carnivora). — Exs.: Dog, Cat, Bear, Otter, Seal. 



6. Cetacea. — Exs.: Whale, Porpoise. 



7. Sea-cows (Sirenia). — Exs.: Dugong, Manatee. 



8. Elephants (Proboscidea). 



9. Conies (Hyracoidea). — Ex.: Syrian Hyrax. 



10. Hoofed Mammals (Ungulata). — Exs.: Tapir, Rhinoceros, Horse, Hippo- 



potamus, Pig, Deer, Cattle, Giraffe, Camel. 



11. Gnawers (Rodentia). — Exs.: Squirrel, Rat, Porcupine, Rabbit. 



12. Edentates (Edentata). — Exs.: Sloth, Armadillo, Ant-Eater, Pangolin. 



B. Metatheria. — The forms embraced by this group have 

 smooth and relatively small cerebral hemispheres. The young 

 are born in a very immature condition, and are usually sheltered 

 for a time in a pouch situated in the abdominal region of the 

 mother. Within this pouch are situated the long teats, to which 

 the young remain attached for some time, and these are so 

 immature as to be at first incapable of sucking, the milk being 

 squeezed into their mouths. Under such conditions they would 

 be in imminent danger of choking were it not that the top of the 



