EXTANT POUCHED ANIMALS. 151 



The Neptunian deposits of these epochs in all quarters of 

 the globe, and even in Europe, contain abundant marsupial 

 remains in great variety, some of them being of very large 

 size. From this we may infer that the extant Pouched 

 Animals are but the last remnant of a group which was 

 once much more widely developed, and which was dis- 

 tributed over the whole surface of the globe. During the 

 Tertiary Period, these succumbed in the struggle for life 

 with the stronger Placental Animals, and the survivors were 

 gradually driven back by the latter into their present 

 restricted area. 



From the Comparative Anatomy of the extant Pouched 

 Animals, very important conclusions may be drawn as to 

 their phylogenetic intermediate position between Cloacal 

 Animals and Placental Animals. The incomplete develop- 

 ment of the brain, especially of the fore-brain {cerebrum), 

 the possession of marsupial bones (ossa marsupialia), the 

 simple structure of the allantois (which does not as yet 

 develop a placenta), with many other characters, have been 

 inherited by the Pouched Animals from Cloacal Animals. 

 On the other hand, they have lost the independent coracoid 

 bone (ps coracoideum) attached to the shoulder girdle. A 

 more important step consists in the fact that a cloaca is no 

 longer formed; the cavity of the rectum, together with the 

 anal opening, is separated by a partition wall from the urinary 

 and sexual opening (sinus urogenitalis). Moreover, all 

 Pouched Animals develop special nipples on the milk-glands, 

 which are sucked by the young after birth. These nipples 

 project into the cavity of a pouch, or marsupium, in the 

 ventral side of the mother. This pouch is supported by 

 a couple of marsupial bones. In it the young, which are 



