EGG-LAYING MAMMALS. 
115 
Tertiary formations of Patagonia. On account of its rarity, no 
example of this animal is at present shown. 
Order XI. MONOTREMATA, or Egg-laying Mammals. 
(Lower Gallery, Case 71.) 
The order Monotremata, like the Marsupialia, represents by 
itself one of the primary sections or subclasses into which 
Mammals are divided. In all their anatomical characters its 
members show a remarkably low type of organization, doubtless 
transmitted more or less directly from some of the earliest 
Mammalian forms. 
Fig. 62. 
The Echidna, or Spiny Anteater {Echidna aculeata). 
Monotremes present many important skeletal characters, 
among which may be specially noticed the peculiar structure 
of the shoulder-girdle, in which the clavicle is large, and 
connected with the sternum by an inter-clavicle ; the 
coracoid, instead of being rudimentary as in other Mammals, is 
large and articulates with the sternum ; and the whole structure 
is of a very low and Reptile-like type. The skull is long and 
