SYSTEM OF NATURE. 
29 
hangs before the penis, which when at rest is directed 
backwards.”—C. R. A. “ Both sexes manifest their affinity 
to the oviparous classes in possessing two superior rente 
cavte, and in the want of the inferior mesenteric artery.” * 
Still more important even than these discrepancies in the 
organs of generation and circulation are those of the brain. 
“We can trace through the different orders the increasing 
complication of this organ, until we find it in man to have 
attained that condition which so eminently distinguishes 
him from the rest of the class. And if the introduction 
of new powers into an organism necessarily requires a 
modification in its mode of development, with what 
other than the perfection of the nervous system can we 
connect true viviparous or placental generation ? for we 
do not perceive that in their digestion, circulation, respi¬ 
ration, locomotion or temperature, the mammiferous Verte- 
brata are in any degree advanced beyond the bird, in con¬ 
sequence of their more complex, or, as it may be termed, 
more careful generation.”f “ Agreeably to this view, con¬ 
nected with the ovo-viviparous generation of the Marsu- 
piata, and with an inferiority of intelligence which Professor 
Owen observed in these animals when in confinement, he 
was induced to undertake a careful examination of the 
brain in the various marsupial animals, and the result of 
this investigation was a most interesting discovery. Be¬ 
sides the decreased size of the hemispheres of the brain, 
and consequent exposure of the cerebellum, indicative of 
a low grade of organization, the corpus callosum and sep¬ 
tum lucidum were found to be entirely wanting in these 
* Owen, Phil. Trans. 1834, p. 333. 
f Owen, Phil. Trans. 1834, p. 359. 
