DonaLpson AND Davis, Human Spinal Cord. 33 
is little variation in the relation between the gray and white, 
and that the change in this relation must occur at some period 
‘after the fifth year. 
In this connection, it is of interest to determine whether 
the growth changes leading to the greater total area of the 
cord segments at maturity are the result of a proportional en- 
largement in the different regions of the cord. In order to de- 
termine this, it is necessary to compute the percentage values 
of the total areas in the different regions. The results of this 
computation are shown in the following table: 
TABLE IX. 
Showing for both the mature and immature cords the percentage value 
which is represented by the total areas of the segments that 
constitute the cervical, thoracic, lumbar and sacral and coccygeal 
regions respectively. 
Region. Age. 
I year. 2 years. 5 years. Maturity. 
Cervical 39-05 36.86 36.60 37.92 
Thoracic 31.85 33-86 33-18 36.30 
Lumbar 16.52 17.02 17.42 17.69 
Sacral and Coccygeal 12.58 12.26 12.80 8.09 
100% 100% 100% 100% 
From the foregoing Table IX, it appears that after the fifth 
year, the proportional growth in area has been slightly more 
rapid in the thoracic region, and less rapid in the sacral and 
coccygeal, while in the two intumescentiae, the relations at ma- 
turity are similar to those found during the first to the fifth 
year of life. From the end of the first year then, the relative 
areas of the different regions of the cord change but slightly 
during subsequent development. The statements which have 
been made on the basis of the total area can also be repeated for 
both the gray and the white substance separately, though it is not 
deemed necessary to publish the computations, as the data for 
them are found in Table VI. 
It must be remembered, however, that from the first to the 
fifth year of year of life, the medulla spinalis is growing rapidly 
