FAMILIES OF MARSUPIALS. 687 



In the embryo, however, there are four upper incisors, of which the 

 first persists, and five lower incisors, of which the third persists. 

 The fore feet have five distinct toes with strong nails : the hind 

 feet have a small nailless hallux, the second, third, and fourth 

 toes partly united by skin, the fifth distinct. The tail is very 

 short. The stomach is simple, the caecum very short. 



There is but one genus Pkcacoloniys^ with three species. 

 Family Phalangeridse : Small woolly arboreal nocturnal Marsupials, 

 with vegetarian or mixed diet. The fore feet have five distinct 

 toes ; the hind feet have a large, nailless, opposable hallux, the 

 second and third toes are narrow and bound together by skin, the 

 fourth and fifth free. The tail is generally long and prehensile. 

 The stomach is simple, the caecum usually large. Average 



3> i> 2-3, 3-4 



dental formula, 



I, O, O-2, 3-4 



Examples : The grey Cuscus (Phalanger orientalis) ; Tarsipes, a 

 small mouse-like animal which feeds on honey, and is remark- 

 able in having no inflection of the angle of the mandible and 

 no caecum ; the flying phalangers (Petaurus], with a parachute 

 of skin extending from the little finger to the ankle ; the 

 Koala or " native bear " (Phascolarctos cinereus], a relatively 

 large form about two feet in length. An extinct form, Thy- 

 lacoleo, of the late Tertiary period of Australia, is interesting 

 in its extraordinary dentition, the functional teeth being reduced 

 to large front incisors and third premolars, both adapted for 

 sharp cutting. 

 Family Macropodidce : Kangaroos, herbivorous terrestrial Marsupials. 



3> O - T > 2 > 4 



Dentition, The incisors are sharp and suited for 



I, O, 2, 4 



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 (Potorous] ; the genus Hypsipryinnodon, 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 Tasmania, 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 hind feet have only four. 

 The hallux is absent ; the fourth toe is very long ; the fifth is about half 

 as large ; the third and second are too slender to be useful for more than 

 scratching, and are bound together by the skin (syndactylous). The 



