168 OSSEOUS, MUSCULAR, AND NERVOUS SYSTEMS 
their own wants and safety. Yet these bones are present 
in the Ornithorynchus and Echidna, which are said not to 
have a marsupium ; and the fact has been brought forward 
by Professor Blumeneach, as a proof of what he calls an 
union of the teleological and mechanical principles in 
the function of generation, — principles which were formerly 
thought to be incompatible with each other/' The forma- 
tion of this anomalous pair of bones (he observes) for the 
purpose of supporting the abdominal pouch of the female, 
is a clear instance of the teleological principle ; that is, it 
shews a peculiar part formed for a certain purpose. Their 
existence in the male (and of course in the Ornithorynchus) 
where the end and purpose of their formation do not exist, 
shews the mechanical principle, as if they had been merely 
framed in compliance with some general model for the 
structure of the species *. 
The bones of the extremities may be described together, 
as they so much resemble each other. The os humeri is 
strong, and peculiarly formed with regard to its processes, 
which are very prominent, and afford a powerful point of 
attachment to the various muscles ; it is perforated near its 
radial extremity, as in many other animals, for the trans- 
mission of bloodvessels. The olecranon of the ulna is much 
developed, and of considerable breadth. In the posterior 
extremity, the fibula bears a strong resemblance to the ulna, 
and has a remarkably strong process for the insertion of 
muscles extending upwards towards the pelvis and tail. 
The tarsal and metatarsal and digital bones of the posterior 
extremities, and the corresponding bones of the anterior 
extremity, do not require any particular description. We 
shall therefore only remark, that, in the construction and 
perfect organisation of the bones of the extremities, the Orni- 
thorynchus differs most remarkably from Birds and E cptiles, 
* A Short System of Comparative Anatomy, p. 4'L 
