OF THE ORNITHORYNCHUS PARADOXUS. 167 
which he has given the name of " Os EpisternaV The 
principal distinguishing characteristic of this " os episternal," 
is said to be, that it is placed always on the coracoid pro- 
cess ; but this rule does not seem to hold true with regard 
to the frog, and perhaps with some other reptiles. We are 
compelled, therefore, to consider these bones as strictly 
belonging to the class Reptiles, and that their presence in 
the Ornithorynchus may depend either on the extraordinary 
anomalies which undoubtedly exist in this animal, or that 
it is connected with the aquatic habits of the animal, and 
intended to facilitate the movements of the anterior extre- 
mity, and to extend them so far as was consistent with the 
safety of the shoulder-joint. In short, it seems intended 
to permit the coracoid process of the scapula considerably 
to change its position, and to approximate or recede from its 
fellow, at the will of the animal, and thereby very much to 
extend the movements of the anterior extremity, and to con- 
vert it into an oar of the most perfect description. 
It is sufficiently curious, that, whilst so much has been 
written to prove the analogy of the bones entering into the 
composition of the sternum, clavicle, and scapula through- 
out the animal kingdom, no attempt, so far as I know, has 
been made to name the bones which may be supposed ana- 
logous to the marsupial bones of the pelvis, and which are 
not peculiar to the ornithorynchus, but found in a very con- 
siderable number of animals *. The truth is, that these 
bones are quite peculiar to the class, and created by Na- 
ture apparently for a particular purpose, viz. of supporting 
the marsupium, or abdominal pouch, in which the young 
of these animals are contained, from the period of their 
imperfect birth, until they are capable of providing for 
* Since wriling the above, I find that an attempt has been made to com- 
pare the marsupial bones with the os peniale found in eertaiji animals, as the 
dog, &c. 
