HIGH SCHOOL ZOOLOGY. 161 



like most of tne ant-eatei'S, and secures its food with its 

 tongue. There are no teeth, at least rudimentary teeth which 

 are present in the emlnyo never break through the jaw, so we 

 are obliged to consider the absence of teeth not as a primitive 

 chai-acter, but as an adaptation to habits of life. 



Inwardly, however, the Monotremes agree with each other, 

 and differ from the other mammals in many important respects, 

 such as the presence of an episternum (III, 18), with which the 

 clavicles articulate, and of complete coracoids, which unite the 

 scajjula and sternum. There are also other features which, 

 like their oviparous habits and the structural characters associ- 

 ated therewith, remind us more of the Sauropsida than the 

 Mammalia ; such are the simplicity of the brain and of the ear, 

 and the temperature of the blood, which is much more like 

 that of the suiTOunding medium than in the oi'dinary mammals. 



18. The Metatheria similarly correspond to a single order, 

 the Marsupialia. This order receives its name from the pouch 

 referred to above (§ 2), which is supported by two epipubic 

 bones, present in all members of the order, whether the pouch 

 is well-developed or not. The Monotremes also have these 

 epipubic bones, so it is probable that they are not formed in 

 connection with the pouch, but rather i-epresent such structures 

 as the fore part of the pelvis in the Menobranch. Although 

 the Marsupials are specially developed in the Australian region, 

 they are not exclusively confined to it, for in America there are 

 several species of opossum {Didelphys), and in the Oriental 

 I'egion also, there are a few representatives of the group. 

 Australia is, nevertheless, the home of the Marsupials of the 

 present day, although it is of interest to note, that the earliest 

 fossil remains of mammals, obtained in Europe and other parts 

 of the world, indicate that they ought to be associated with the 

 Metatheria instead of the Eutheria, and, therefore, that this 

 sub-class was at one time much moi'e widely distributed than it 

 now is. 



