690 



MAMMALIA. 



large form, about 2 ft. in length. An extinct form, Thyla- 

 coleo, of the late Tertiary period of Australia, is interest- 

 ing in its extraordinary dentition, the functional teeth being 

 reduced to large front incisors and the third premolars, both 

 adapted for sharp cutting. 

 %J 4. Family Macropodida?. — Kangaroos, herbivorous terrestrial Mar- 

 supials. Dentition, 3 ' ""'' 2 ' 4 . The incisors are sharp, and 



suited for cropping herbage. The hind-legs are usually larger 

 than the fore-legs, and the animals move by leaps. 

 Examples. — The true kangaroos, e.g. Macropus; the rat-kangaroos 

 or potoroos (Potormis) ; the genus Hy- 

 psiprymnodon, with a foot approaching 

 that of the Phalangers. 

 The true kangaroos, belonging to the genus 

 Macropus, include the largest living Marsupials ; 

 but within the genus there is much difference in 

 size. 



The grey kangaroo (M. giganteus) lives on 

 the grassy plains of Eastern Australia and Tas- 

 mania, and is as tall as a man ; the Wallabies, at 

 home in the bush, are smaller, and some are no 

 bigger than rabbits. 



The hind-limbs seem disproportionately long, 

 and are well suited for rapid bounding. The 

 long tail, carried horizontally, helps to balance 

 the stooping body as the animal leaps, and it 

 gives additional stability to the erect pose. The 

 fore-limbs sometimes come to the ground when 

 the animal is feeding, and in the largest species 

 they are strong enough to throttle a man. 



The fore-limbs bear five clawed digits ; the 



Fig. 302. — Foot of hind-feet have only four. The hallux is absent ; 



young kangaroo. the fourth toe is very long ; the fifth is about 



2, 3, Small syndactylous half as large ; the third and second are too 



' toes ; 4, large fourth slender to be useful for more than scratching, and 



toe ; Si fifth toe. are bound together by the skin (syndactylous). 



The length of the hind-limb is due to the tibia 



and fibula, and to the foot. The clavicles and fore-arm are well 



developed. The epipubic or marsupial bones are large. 



The kangaroos feed on herbage, and are often hunted down on 

 account of the damage which they do to pastures and crops. The sharp 

 incisors are suited for cropping the grass and herbs, which the ridged 

 and tuberculated molars crush. 



As the kangaroos are exclusively herbivorous, it is not surprising to 

 find that the stomach is large and complex, with numerous saccules on 

 its walls. The whole gut is long, and there is a well-developed 

 CEecum. 



Numerous fossil forms related to the kangaroos are found in 

 Australia, some considerably larger than the existing forms. The 

 gigantic Diprotodon australis, which was as large as a rhinoceros, is 



