4 CLASSIFICATION OF THE MAMMALIA. [chap. 



b. The cushion-footed, or Tylopoda, the Camels and Llamas. 



c. The Tragulina, or Chevrotains, a group of little deer-like 

 animals formerly associated with the Musk-deer. d. The 

 Pecora, or true Ruminants, comprising the Deer, Giraffes, 

 Antelopes, Sheep, Goats, and Oxen. The last three divisions 

 constitute the order Ruminantia of Cuvier. 8. Hyra- 

 coidea, an order consisting of a single genus, Hyrax, a small 

 animal having many affinities with the Perissodactyle Un- 

 gulata, with which it is often associated. 9. Probosctdea, 

 represented at present only by the two species of Elephant ; 

 and 10. Rodentia, a well-marked group, but with varied 

 affinities, both to the Insectivora and Primates on the one 

 hand, and to the Ungulata and Proboscidea on the other, and 

 also to the Didelphia. This order contains the Hares, Rats, 

 Guinea-pigs, Porcupines, Beavers, Squirrels, &c. 



II. The sub-class Didelphia contains only one order, 

 Marsupialia, consisting of animals presenting great diver- 

 sity of superficial appearance and habits of life, although 

 all united by many essential anatomical and physiological 

 characters. The young are born in an exceedingly rudi- 

 mentary condition before the formation of a placenta, and 

 are transferred to the nipple of the mother, to which they 

 remain firmly attached for a considerable time, nourished 

 by the milk injected into the mouth by compression of the 

 muscle covering the mammary gland. The nipples are 

 nearly always concealed in a fold of the abdominal integu- 

 ment, or " pouch " {inarsufiium), which serves to support 

 and protect the young in their early helpless condition. 

 The existing species are entirely confined to Australia, its 

 neighbouring islands, and the American continent ; though, 

 in former times, they had a more extensive geographical 

 range. The Wombats, Kangaroos, Phalangers, Koalas, 



