r jaws do not protrude so greatly. It, too,
is semi-erect, so that the line of the vertebral axis makes an angle with
the plane of the ground of about seventy degrees. Its anterior limbs, or
arms, are again very long and bulky; and like the chimpanzee, it rests its
knuckles upon the ground in walking.

It is a short step further to the human organism, whose brain has become
larger and more complex, with a corresponding advance in the functional
powers of reason and the like that owe their existence to the improved
structural basis. After what has been said earlier regarding the relation
between the erect attitude in walking and the increased size of the
cranial part of the skull as compared with the face, it will not be
difficult to see how inevitably the former is the result of the latter.
Should we get upon the ground upon our hands and knees in the position of
a tailed monkey, the eyes look straight into the ground, for the bulging
cranium has pushed out over the jaws and face so that they lie _under_ the
brain-case instead of in front. A person in this position can bend back
the head so as to look ahead, but the strain is too great for comfort.
Rising to the knees, and lifting the hands from the ground, a feeling of
ease at once succeeds that of tension. In the course of evolution
accomplished primarily by the increase of the higher portions of the
brain, the erect position has been assumed gradually and naturally, and to
maintain it has necessitated many other changes in skeleton and muscles;
for example, the pelvis has broadened to support the intestines, which
bear downwards instead of upon the abdominal walls; a double curve has
arisen in the axis of the vertebral column, giving an easier balance to
the upper part of the body and the head. Countless structures of the human
frame testify to an originally four-footed position and to a rotation of
the longer axis through an angle of ninety degrees, as evolution has
produced the human type.

The conclusion that the human brain has made mankind is thus established
as one of fundamental importance. Proceeding further, we learn that this
organ proves to be essentially the same as the brain of lower primates; it
does not gain its greater size and efficiency by the origination of wholly
new and unique parts, but solely by the further elaboration of the ones
present in lower forms. In a word, it is only a difference in _degree_ and
not in essential _kind_ that separates m