90 Miss M. P. FitzGerald. Tlie Lumbosacral-coccygeal [June 17, 



For taking the measurements of the drawings Amsler's planimeter No. 3 

 was used, so adjusted that one division on the disc indicated 100 sq. cm., 

 and in those cases where the areas to be measured were very small the 

 planimeter was set so that one division on the disc indicated 20 sq. cm. 

 Every care was taken to obtain accuracy. In the majority of cases the 

 pointer was carried five times round the area to be measured, and ten or 

 more times when the areas were small. To guard against accidental errors 

 the planimeter reading was always taken after completing the first circuit, 

 and the result compared with that obtained by dividing the final reading 

 by the number of times the pointer had been carried round. The difference 

 was in all cases within the limits of instrumental error. 



In each case the total area of the cross-sections of the cord was first 

 determined. The sectional areas of the dorsal columns, the ventro-lateral 

 columns, and the grey substance were then each measured separately in 

 •each half of the cord, the sum of the two halves being taken as the measure- 

 ment of the whole. 



The total area of the central canal was measured independently of the 

 grey substance, and the results are given in Tables II, VI. These measure- 

 ments are not separately represented in the charts, though it is necessary to 

 take them into account in explaining the form of some of the curves. 



The difference between the sum total of the measurements of the com- 

 ponent parts of the cord and of the total section area was, in each case, noted 

 as " error." As a rule the error was negative, its average value being 

 - 2 per cent. This may be regarded as due to " personal equation." 



The total sectional area of the white substance was obtained by adding 

 together the figures obtained for the dorsal and the ventro-lateral columns. 



It must be here stated that the term " ventro-lateral " columns is used in 

 this paper to signify the whole of the white substance ventral to Lissauer's 

 ""marginal zone." Lissauer* regarded this zone (Waldeyer's " Markbriicke ") 

 as belonging to the dorsal horn and forming a bridge between the dorsal and 

 lateral strands of the white substance. It has therefore been used as 

 a boundary between the two portions of the white substance, and has been 

 measured with, and as a part of, the grey substance. 



For measuring the grey substance in each half of the cord, the division 

 was made by continuing a line from the dorsal median septum to the dorsal 

 boundary of the central canal, and from the ventral boundary of this to the 

 ventral median fissure. The grey substance was subsequently subdivided for 

 the purpose of obtaining information as to the relative development of the 

 " dorsal " and of the " ventral " horns. Since no actual boundary exists 

 * Lissauer, ' Archiv f. Psychiatrie u. Nervenkrankheiten,' vol. 17, 1886. 



