MAMMALIA. 641 



chamber, so that there is still but a single vent, a circumstance 

 from which the name of the order is derived. 



Even their skeleton, in many points, presents a very close affinity 

 to that of a Bird, as will be evident on examining the osseous sys- 

 tem of the Ornithorhynchus paradoxus (Jig. 297). 



Fig. 297. 



The mouth of this quadruped indeed resembles that of a Duck, 

 whence the name of " Duck-bill," whereby it is usually distin- 

 guished. It has, moreover, a distinct furcular bone in addition to 

 what would seem to be the ordinary clavicles ; but in reality these 

 are the coracoid bones still largely developed. Moreover, the an- 

 terior or sternal ribs are ossified, and a spur is attached to the hind 

 foot of the male, not remotely resembling that of a Cock : this last 

 appendage is perforated by a duct, and has a gland connected with 

 it, situated on the inner side of the thigh, by which a poisonous 

 secretion was formerly supposed to be elaborated. 



(722.) The MARSUPIALIA, it will be afterwards explained, as 

 regards the conformation of their generative system, are organized 

 in accordance with a type intermediate between that common to 

 Birds and that which characterizes Mammalia properly so called. 



The Marsupial quadrupeds bring forth their young alive, but in 

 such an imperfect condition, that at the period of their birth 

 scarcely the vestiges of their limbs have become apparent ; and in 

 this state they are conveyed into a pouch formed by the skin of the 

 female's abdomen, where they fix themselves by their mouths to 

 the nipples of their mother, and, sucking milk, derive from this 

 source the materials for their growth. These animals are peculiar 

 to the Australian and American continents; nay, in Australia, so 

 anomalous in all its productions, with one or two exceptions, and 

 those perhaps brought there by accidental importation, all the 

 quadrupeds are constructed after the Marsupial type. The great 

 characteristic whereby to distinguish the skeleton of a Marsupial 



