160 DOCTRINE OF EVOLUTION 



as a subject for comparative structural study, the third 

 and fourth characters do not concern us here ; but it is 

 well to point out that they depend entirely upon the 

 second, and that they are the functional concomitants 

 of the improved type of brain belonging to the highest 

 type. Two characters remain, and in both cases it is 

 significant that differences in degree only are to be 

 found by even the closest analysis. The human brain 

 is the same kind of brain that lower primates possess ; 

 its structure is unique in no general respect. And as 

 regards the first-mentioned character, comparative 

 anatomy shows, in the first place, that this also is 

 something differing only in degree, and in the second 

 place, that it is due directly to the development of the 

 brain. For these reasons a survey of the various 

 members of the order of primates must deal largely 

 with the progressive elaboration of the brain and the 

 entailed effects of this enlargement. 



The order of primates is subdivided as follows : — 



Sub-order 1. PRO SI Mil. Lemurs. 

 Sub-order 2. ANTHROPOIDEA . 



Family 1. Hapalidce. The marmosets. 



Family 2. Cebidce. The American or tailed 

 monkeys. 



Family 3. Cercopithecidce. The baboons. 



Family 4. Simiidce. The true apes. 



Family 5. Hominidce. The human species. 



Each one of these subdivisions is interesting in its 

 own way, either because its members depart from the 

 typical condition of the whole order in some respects, 

 or because of some character that foreshadows and leads 



