DonaLpson AND Davis, Human Spinal Cord. 29 
so closely that for the areas of the nerves, as does the curve 
based on the areas of the gray substance in the five-year old 
cord. Especially in the thoracic and lumbar regions, the area 
of the gray substance is larger in proportion to the cross sec- 
tions of the nerves than in the case of the young cord. In gen- 
eral there appears to be in the mature cord, as contrasted with 
that of the child, a shift of the larger areas of the gray substance 
one or two segments cephalad. As a consequence, therefore, 
using data derived entirely from mature individuals, the curves 
are less similar than the figure of Liprrirz (Fig. 2, p. 478) 
would indicate. 
If we now compare the relative development of the volumes 
of the successive segments of the cord, with the areas of the 
cross sections of the spinal nerves, we find that while there is a 
fair correspondence in the cervical and in the sacral regions, 
that in the thoracic and upper lumbar regions, where the seg- 
ments have grown most in length, a great disparity exists be- 
tween the volume of the gray substance and the area of the 
cross sections of the nerves, the gray substance being much 
more abundant than we should expect. This suggests that in 
these localities, the lengthening of the segments, and conse- 
quent increase in the volume of the gray substance, is merely 
one of adaptation to the elongation of the vertebrae, and not 
accompanied by any corresponding increase in the complexity 
of its structure. 
D. GROWTH CHANGES. 
I. On the Areas of the Cross Sections of the Several Segments 
of the Spinal Cord at Different Ages. 
For this comparison we have used as a standard the rec- 
ords which were employed for the composite curve in Chart I. 
As previously explained, the data for this composite curve were 
obtained by taking the average of the observations on the four 
individuals used for the construction of curves A, B, C, D re- 
spectively of Chart I. The numerical data are given in the 
column headed ‘‘Mature”’ tn Table VI. 
To compare with the composite curve we have from 
