go far
towards justifying the opinion of hereditary connexion. At the same
time, the comparison brings into view differences in human structure
adapted to man's pre-eminent mode of life, though hardly to be accounted
its chief causes. It may be seen how the arrangement of limbs suited for
going on all-fours belongs rather to the apes than to man, and walking
on the soles of the feet rather to man than the apes. The two modes of
progression overlap in human life, but the child's tendency when
learning is to rest on the soles of the feet and the palms of the hands,
unlike the apes, which support themselves on the sides of the feet and
the bent knuckles of the hands. With regard to climbing, the long
stretch of arm and the grasp with both hands and feet contribute to the
arboreal life of the apes, contrasting with what seem the mere remains
of the climbing habit to be found even among forest savages. On the
whole, man's locomotive limbs are not so much specialized to particular
purposes, as generalized into adaptation to many ends. As to the
mechanical conditions of the human body, the upright posture has always
been recognized as the chief. To it contributes the balance of the skull
on the cervical vertebrae, while the human form of the pelvis provides
the necessary support to the intestines in the standing attitude. The
marked curvature of the vertebral column, by breaking the shock to the
neck and head in running and leaping, likewise favours the erect
position. The lowest coccygeal vertebrae of man remain as a rudimentary
tail. While it is evident that high importance must be attached to the
adaptation of the human body to the life of diversified intelligence and
occupation he has to lead, this must not be treated as though it were
the principal element of the superiority of man, whose comparison with
all lower genera of mammals must be mainly directed to the intellectual
organ, the brain. Comparison of the brains of vertebrate animals (see
BRAIN) brings into view the immense difference between the small, smooth
brain of a fish or bird and the large and convoluted organ in man. In
man, both size and complexity contribute to the increased area of the
cortex or outer layer of the brain, which has been fully ascertained to
be the seat of the mysterious processes by which sensation furnishes the
groundwork of thought. Schafer (_Textbook of Physiology_, vol. ii. p.
697) thus defines it: "The cerebral cortex is the seat of the