68 J, D. Dana on the Classification of Mammals. 
being 
both of the natural and intellectual philosopher. 
This cephalization of the human system has been recognized 
by Carus; but not in its connection with a deep-rooted structural 
law pervading the animal kingdom. It is the comprehensive 
ness of the law which gives the special fact its great weight. - 
Aristotle, in his three groups of Mammals, the Dipoda or two- 
footed, the Tetrapoda or four-footed, and the Apoda or footless 
species, expresses distinctions according with this law. The 
term Dipoda, as applied to Man, is far better and more philo- 
sophical than Bimana. 
The erect form of the structure in Man, although less author- 
itative in classification, is a concomitant expression of this cepha- 
lization. For the body is thus placed directly beneath the brain 
or the subordinating power, ped i no part of the structure is either 
anterior or posterior to it. Two feet for locomotion is the small- 
est possible number in an animal. Cephalic concentration and 
posterior abbreviation are at their maximum. ‘The characters 
of the brain distinguishing the Archencephala (Man) in Prof. 
Owen’s system, so far as based on its general form or the relative 
position of its parts, flow from the erect form. 
an’s title to a position by himself, separate from the other 
Mammals in classification, appears hence to be fixed on structural 
as well as psychical grounds. 
The other Mammals are either true viviparous species, or semt- 
oviparous. 
The latter, including the Marsupials and Monotremes, constitute 
a natural group, as usually so regarded, the most fundamen 
characteristic of which—the immaturity of the young at birth, 
by which they are related to oviparous Vertebrates—suggests 
the name OOTIcorDs. 
e viviparous species are variously arranged by different 
zoologists.‘ Prof. Owen, basing his subdivisions largely, as has 
been stated, on the characters of the brain, makes the two groups 
Gyrencephala and Lissencephala,—the former so named from 
having, in general, the surface of the brain es and the 
F , id 6 
m its being, with some exceptions, smoo 
- See Professor Owen’s memoir already referred to for an account of different 
earlier systems of the Classification of Mammals, 
* See this Journal, 
vol. xxv, pp. 178, 179, for the precise characters of these 
