210 EDWARD HORNE CRAIGIE 
the normal tables for the albino rat (Donaldson, 15, table 68), 
which give the following results: 
BRAIN WEIGHT | BRAIN WEIGHT 
RAT SEX BODY LENGTH | BODY WEIGHT eye ges las Seen one 
LENGTH WEIGHT 
mm. grams grams grams 
3l of 200 _ 228.4 1.858 1.900 
55 9 185 159.2 1.782 1.773 
56 je) 198 197.4 1.841 1.835 
a8 rot 210 234.8 1.903 1.907 
It is thus evident that the female brains may be regarded as 
slightly smaller than those of the males. Since the vascularity 
of the cerebral cortex is poorer in the female brain, rather than 
richer, the sexual difference cannot be explained upon the basis 
of size in the manner suggested above. 
Since measurements were not recorded for the Toronto ani- 
mals, a similar scrutiny cannot be applied to the comparison of 
local groups. It seems not improbable that the difference in 
this case may be capable of explanation on the above basis, 
though this would not account for the greater difference found 
in the cortex as compared with the subcortical regions. 
While one must hesitate to generalize upon only two com- 
parisons with the limitations already pointed out, these data 
seem to suggest a greater susceptibility in the cortical vasculari- 
zation than in that of the more ancient portions of the central 
nervous system to differences either within or without the body 
—sexual, hereditary, or environmental. 
The writer is much indebted to Dr. H. H. Donaldson, of The 
Wistar Institute, who kindly read the manuscript and made a 
number of valuable suggestions regarding the presentation of 
the material. 
SUMMARY 
1. The vascularity of each of the five distinguishable layers 
in five different areas of the cerebral cortex has been measured 
in eight albino rat brains out of the ten which were used in the 
prosecution of a study, already reported (Craigie, ’20), upon 
