CHAPTER XIII 



MAMMALIA 

 Scheme of Classification 



Prototheria, egg-laying mammals, restricted at the present day to 

 Australia and New Guinea. 



Ornithorkynchus , Echidna. 



MetatheriA; mammals in which the retention of the young within the 

 uterus is much less prolonged than in the ordinary mammals. 

 Opossums (N. and S. America), Australian Marsupials. 



EuTHERiA, t5rpical mammals. 



Edentata (Ant-eaters, Sloths and Armadillos of the New World ; 

 Scaly Ant-eaters and Aard-vark of the Old World) ; Proboscidea 

 (Elephant) ; Hyracoidea (Cony) ; Ungulata (Horse, Tapir, Rhino- 

 ceros, Hippopotamus, Pig, Camel, Deer, Giraffe, Ox, Sheep, Ante- 

 lope) ; Sirenia (Manati and Duyong — highly specialized aquatic 

 mammals) ; Cetacea (Whales) ; Carnivora (Cats, Dogs, Bears, Seals) ; 

 Rodentia (Beaver, Rats, Cavies, Porcupine, Rabbit) ; Insectivora 

 (Hedgehog, Mole, Shrew) ; Cheiroptera (Bats) ; Primates (Lemurs, 

 Monkeys, Apes, Man). 



Later portions of the medical curriculum will be devoted to intensive 

 study of structure and function in Man — a typical example of the group 

 Mammalia — ^and this chapter will consist merely of a few introductory 

 remarks upoii the general characteristics of the Mammalia. 



While the Mammalia in the general plan of their organization have 

 perhaps not reached such a high level of specialization as have the Birds 

 there are three features in which they stand pre-eminent amongst verte- 

 brates. The first of these is brain-power: in no other group of verte- 

 brates is there anything like the high degree of psychical development 

 found in the mammals ; in no other group is there such skilled brain- 



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