Measurement of the twelve thoracic and five lumbar vertebrae of twenty-one normal spines and of one scoliotic spine, ranging in age from six to eighty-six, elicited the following conclusions:

1. The postnatal development of normal spines becomes asymmetric about the age of six, progressing with advancing age.

2. The asymmetry concerns the vertebral body and pedicles as well as the arches. The most striking feature of the asymmetries found was the dorsoventral elongation of the vertebral bodies: in the upper thoracic region, on the left; in the lower thoracic segment, on the right; and in the lumbar region, on the left. Besides this, the lengthening of the pedicles on the side of the elongation and broadening of the pedicles on the other side, and the deviation of the arches opposite the side of the dorsoventral elongation could be regularly observed.

3. Since the spine in all of the specimens except that of the normal six-year-old child showed marked lateral deviation, the asymmetric postnatal development of the spine represents physiological scoliosis.

4. In physiological scoliosis, contrary to the findings in pathological scoliosis, the wedging of the vertebrae plays but a subordinate rôle. The curves throughout are composed of lozenge-shaped (rhombic) vertebrae, representing the prescoliotic stage of the deformation without marked signs of motion in the articular processes. Further differences between physiological and true scoliosis are as follows: In physiological scoliosis the physiological sagittal curves never disappear, and, furthermore, in none of the specimens examined were all of the bone elements of the same vertebra concerned at the same time; in true scoliosis all of the parts of the vertebra are more or less deformed.

5. The osteophyte production always starts at the ventral edge of the dorsoventral elongation.

6. In physiological scoliosis, as well as in pathological scoliosis, the deformation of the spine takes place in the diagonal plane, never in the exact frontal plane.

7. The cause of physiological scoliosis is the human gait, which forces the spine into a threefold curve, alternately changing at every step. However, the innate normal asymmetries of the human body eventually establish permanent lateral curves of the spine, showing marked individual variations within the general law.