markedly different from those of other orders.  The number of digits is always five, and with few exceptions they bear nails instead of claws.  The clavicles, or “collar bones,” are well developed in correlation with the prehensile nature of the fore limbs; a bony ring surrounds the orbit or eye socket.  Finally there are two mammary glands by which the young are suckled.  It is because any other details of difference between man and other forms are far less marked than the agreements in these respects, that the human species must be regarded as a primate mammalian vertebrate.

* * * * *

The comparative study of the human organism as a structural type has now been narrowed down to a review of the various members of the order of primates.  It is the duty of science to arrange these organisms according to the minor differences beneath the agreements in major qualities, and to show how they are related in an order of evolution.  It will appear, when this is done, that the supreme place is given to the human species on account of four and only four characteristics; these are (1) an entirely erect posture, (2) greater brain development, (3) the power of articulate speech, and (4) the power of reason.  As we are treating the human body 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. PROSIMII.  Lemurs. 
Sub-order 2. ANTHROPOIDEA. 
  Family 1. Hapalidae.  The marmosets. 
  Family 2. Cebidae.  The American or tailed monkeys. 
  Family 3. Cercopithecidae.  The baboons. 
  Family 4. Simiidae.  The true apes. 
  Family 5. Hominidae.  The human species.  Primates

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 to a more developed element of the animals placed in the higher sections.