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.