﻿22o ALLIENS NATURALISTS LIBRARY. 



process of the blade-bone, there are on each side two distinct 

 bones lying on the inferior aspect of the skeleton, and con- 

 nected with the former. Of these, the most anterior, as 

 representing the coracoid process of the blade-bone, may be 

 termed the coracoid ; while the posterior element may be called 

 the metacoracoid. Both these pairs of bones exist in certain 

 extinct Reptiles ; while the hinder pair are represented in Birds, 

 where they are commonly termed the coracoids. The 

 metacoracoids, it should be added, are articulated with the 

 breast-bone, or sternum, as in Birds. 



The brain, although of a distinctly Mammalian type, is very 

 simple ; and has the connecting cross-fibres on the lower sur- 

 face known as the corpus callosum, either very slightly 

 developed, or not present at aU ; Mr. A. Hill, who is one of 

 the latest investigators on the subject, believing in the complete 

 absence of the structure in question. The minute bones 

 occurring in the interior of the ear are hkewise of a much 

 simpler type than in other Mammals ; and they once more 

 show the affinities of these creatures to the lower classes of 

 Vertebrates. 



The above are some of the most important features which 

 justify the separation of the Monotremes not only as an Order, 

 but likewise as a distinct Sub-Class ; and they serve to show 

 how very widely the group differs from all other Mammals. It 

 is true that they agree with the latter in the circumstance that 

 the young are nourished by means of milk-secreting glands \ 

 but if Gegenbaur be right in his view that these glands in the 

 Monotremes are not homologous with those of other Mammals, 

 it follows that the milk-secreting function is of no classi- 

 ficatory value whatever ; the presence of these glands in the 

 Monotremes on the one hand and in the higher Mammals on 

 the other being an instance of that parallelism in development 

 to which allusion has already been made. If, therefore, any 



