274 



ANATOMY OF VERTEBKATES. 



hornlike form, in advance of the ' corpus striatum.' The super- 

 ficial grey matter of the cerebrum, through the number and depth 

 of the convolutions, attains its maximum of extent in Man. 



Peculiar mental powers are associated with this highest form of 

 brain, and their consequences strikingly illustrate the value of 

 the cerebral character ; according to my estimate of which, I am 

 led to regard the genus Homo as not merely a representative of 

 a distinct order, but of a distinct subclass of the Mammalia, for 

 which I have proposed the name of ^ Archencephala.' ^ 



150 



Vertical section of tlie adult human brain. (After Arnold.) Half natural size. 



With this preliminary definition of the organic characters, 

 which guide to a conception of the natural primary groups of the 

 class Mammalia, 1 next proceed to define those of secondary im- 

 portance, or the subdivisions of the foregoing subclasses. 



§ 174. Characters of Orders. — In the Lyencephalous Mammalia 

 some have the optic lobes less definitely divided into ' corpora 

 quadrigemina ' than others. Those Avith the more simple optic 

 lobes are ' edentulous ' or without calcified teeth, are devoid of 

 external ears, scrotum, nipples, and oviducal fimbria? ; they are 



^PX'w, I overrule ; fy-^ecpa^os, brain. 



