98 Miss M. P. FitzGerald. The Liimbo-sacr'al-coccygeal [June 17, 



decreases from the latter region to the end of the cord. The increase in the 

 white substance (W) is not so great as that of the grey substance (G). 



There is very little alteration in the section area of the white substance 

 through the first and the greater part of the second lumbar regions, but a 

 marked increase takes place between the lower portion of the third and the 

 fourth and in the fourth lumbar region. The chief development of the 

 white substance extends through the fourth and the upper portion of the 

 fifth lumbar region. The maximum (12 - 68 sq. mm.) being reached in the 

 lower portion of the fourth, is thus found in the same region as the maximum 

 section area of the cord. 



The decrease is rapid in the greater part of the fifth lumbar, the section 

 area of the white substance in the lower part of this region (10 - 48 sq. mm.) 

 being about the same as that in the first lumbar. 



Attention must be drawn to the fact that whilst this marked decrease is 

 taking place in the section area of both the white substance and of the cord 

 in the fifth lumbar region, the section area of the grey substance is still 

 increasing. 



The rapid diminution of the section area of the white substance continues 

 to the seventh lumbar region ; after this the decrease is gradual. 



From the seventh lumbar to the third sacral region (lower) the section area 

 of the white substance (W) is only slightly greater than that of the grey 

 substance (G), whilst from the fourth sacral region to the end of the cord 

 the section areas of the two substances are almost the same. 



In Chart I, and in the above description, the white substance (W) has 

 been regarded as a whole. Through the remainder of the paper it is also 

 dealt with in two distinct parts — i.e.. dorsal columns and ventro-lateral 

 columns. The latter term is here used, as before stated (p. 90), to signify the 

 whole of the white substance other than the dorsal columns. By this means 

 it is possible to obtain information as to the relative value of the contributions 

 made to the white substance of the cord by dorsal roots and by central grey 

 substances resjDectively.* 



The section areas of the dorsal columns and of the ventro-lateral columns 

 are shown in the following chart (II) : — 



* It must be remembered that, owing to the presence of some endogenous fibres 

 amongst those of extra-spinal origin in the dorsal columns, the comparison can only be 

 regarded as of general value. 



