Reginald J. Gladstone 
109 
by broken lines, although having a wider frontal region, had a less tnaximnm 
transverse or interparietal diameter. The total area of the latter is greater than 
the former, as is indicated by the circumference, which is 543 mm. in the broken 
tracing as compared with 530 mm. in the continuous. The product of the two 
principal diameters of the continuous tracing {L = 1S1 x B — Ibo) is 28,055, 
whereas that of the broken curve (i = 182 x B = 150) is 27,300, or 755 less than 
the continuous. The product of the diameters thus gives in this case an erroneous 
indication of the area enclosed by the tracings*. We have accordingly made use of 
the horizontal circumference, although discarding the longitudinal and transverse 
arcs for the reasons stated above. 
The correlation between brain-weight and the outside measurements of the 
head is naturally not nearly so close as that which exists between the outside 
measurements of the skull and the capacity of the skull. For in addition to varia- 
tions in the thickness and shape of the skull, we have to deal with variations in 
the thickness of the scalp and hair, and also with the very considerable variations 
in the amount of space which exists between the surface of the brain and the 
internal surface of the skull. Moreover the weight of the brain is modified by 
variations in density!", the size of the cerebral ventriclesj, and by the amount of 
blood contained in its vessels. 
The weight of the brain also, as is well known, varies considerably with age, a 
progressive decrease of weight and most ]irobat)ly also of size taking place after 
middle age. This decrease, however, appears according to both Boyd's^ and 
Vierordt's|| statistics, to commence at a much earlier age, the highest average braiu- 
weights for different ages occurring between 14 and 20 in both sexes. 
The brain in children and in youth is both actually and relatively to the body 
weight and stature very large. According to Vierordt's statistics, the average 
brain-weight of 35 boys, between 12 and 16 years of age inclusive, was as much as 
1423 grammes ; and in a table published by the same author, showing the average 
brain-weight for each year from birth up to the age of 25, the highest average 
brain-weights, 1490 grm. (/, and 1345 grm. occur at the ages of 15 and ]4 
respectively ; whereas, according to Boyd's statistics, the average brain-weights of 
adult British subjects (mostly of the lower classes), are : 
Males between 20 and 40 1360 grm. ov 48 oz. 
FemalcM „ 20 and 40 1230 grm. or 43i oz. 
[* The problem really is which gives the better average result. It may be worth noting that the 
volume of an ellipsoid is proportional to the diametral product, but not to the product of the three 
circumferences. Ed.] 
t According to Professor Donaldson's statistics, " the average specific gravity of the entire encephalon 
should be for the adult male 1 0363, and for the adult female 1-0360." H. H. Donaldson: Growth of 
the Brain, p. 95. 
X "The cast of the ventricles as made by Welcker displaces 26 cm.'' of water so that the fluid 
filling such a cavity would weigh a trifle over 2(5 grammes." H. H. Donaldson : Growth of the 
Brain, p. 87. The specific gravity of the cerebro-spinal fluid is about 1-009. 
§ See table compiled from the observations of K. Boyd, Pliil. Tranx. 1860, in Quain's Anatomi/, 
Vol. ni. Part i. p. 178. 
II Table 17, p. 104, H. H. Donaldson: The Growth of the Brain. 
