4 o8 



ORDERS OF MAMMALIA. 



to the order. Within the marsupium are contained the nipples, 

 which are of great length. Being for some time after their 

 birth extremely feeble, and unable to perform the act of suc- 

 tion, the young within the pouch are nourished involuntarily, 

 the mammary glands being provided with special muscles 

 which force the milk into the mouths of the young. At a 

 later stage the young can suckle by their own exertions, and 

 they leave the pouch and return to 

 it at will. In a few forms there is 

 no complete marsupium as above 

 described ; but the structure of the 

 nipples is the same, and the young 

 are carried about by the mother, 

 adhering to the lengthy teats. 



The so-called " marsupial bones " 

 (fig. 336) doubtless serve to support 

 the marsupial pouch and its con- 

 tained young, but this cannot be 

 their sole function, since they occur 

 in the Monotremes, in which there 

 is no pouch. 



They consist of two small bones, 

 which spring from the brim of the 

 pelvis, and which are merely ossi- 

 fications of the internal tendons of 

 the "external oblique" muscles of 

 the abdomen. 



The Marsupialia may be pri- 

 marily divided into the vegetable- 

 eating and the rapacious or car- 

 nivorous forms the former characterised by the rudimentary 

 condition or absence of the canine teeth, the molars mostly 

 having broad grinding crowns ; whilst in the latter there are 

 well-developed canines, and the molars mostly have trenchant 

 edges. In the phytophagous section are the living Kangaroos 

 (MacropodidcR\ the Wombat (Phascofotnys), the Kangaroo-rats 

 (Hypsiprymnus), and the Phalangers (Phalangistidcf). In the 

 carnivorous section are the true Opossums (Didelphida), the 

 Banded Ant-eater (Myrmecobius), the T/tytacinus, and the 

 " native devil " or Dasyurus. 



As regards their distribution in time, the Marsupialia pro- 

 bably constitute the oldest of the Mammalian orders. Owing, 

 however, to the detached and fragmentary condition of almost 

 all Mammalian remains consisting in many cases of the 

 ramus of the lower jaw, or of separate teeth it is not possible 



Fig. 336. One side of the pel- 

 5 of a Kangaroo, showing the 

 After 



"marsupial bones" (>) 

 Owen. 



