228 LLOYD'S NATURAL HISTORY. 
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 j 
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 4 
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- 4 
face known as the corpus callosum, either very slightly + 
developed, or not present at all; 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 likewise 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, 7 
but likewise as a distinct Sub-Class ; and they serve to show 4 
how very widely the group differs from all other Mammals. It ° 
is true that they agree with the latter in the circumstance that 1 
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 ‘ 
