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De. Cunningham—Surface Anatomy of the Primate Cerebrum. 181

we may consider that it becomes absolutely fixed at the close of the intrauterine
period of life. Very different, however, are its relations to the coronal
suture at different periods in its history. The figures obtained, it is true,
are somewhat puzzling and difficult to interpret, but one point is perfectly
clear, and it is this :—The parietal bone and the area of brain immediately
subjacent do not grow at an equal pace. In the early stages of its development
the fissure of Rolando lies close to the coronal suture, but this does
not mean that it lies far forward on the brain, but simply that the parietal
bone forms at a later stage a relatively greater extent of the cranial vault.
The maximum amount of the frontal lobe (the district in front of the fissure
of Rolando) covered by the parietal bone is reached at the third month of
extra-uterine life. The upper corono-Rolandic index at this period is 18 "6
and the lower 12"8. From this stage on the coronal suture in its upper
parts falls back a little, and after a slight oscillation it assumes, at the
fourth or the fifth year of childhood, a fixed position with reference to the
fissure of Rolando. This is expressed by the index 16*5. The lower end
of the suture shows changes in its position with reference to the fissure of
Rolando which are less easy to understand. I cannot believe that the
oscillations which are exhibited in the lower corono-Rolandic indices give
expression to the usual growth changes. If we exclude from consideration
all those indices which have been obtained from less than six observations,
we find a steady increase in the index from the earliest periods up to adult
life, viz. 3*6, 10'7, 11-3, 12"9. This, considering the fixity of the lower
end of the fissure on the surface of the hemisphere, bespeaks a slow forward
movement of the lower part of the suture. We know this to be the case.
In the previous chapter we have had frequent occasion to refer to the
circumstance which is chiefly responsible for the forward movement of the
lower portion of the external coronal line. We have noted the gradual
growth forwards of a squamous process from the lower part of the anterior
border of the parietal bone. This overlaps the hinder border of the frontal
bone, and shifts the external suture in a forward direction. The series of
skulls figured in pages 119-122 illustrate this growth-change. Still anyone
who examines a number of skulls must observe that the squamous process
of the parietal varies greatly in extent. Sometimes fully half an inch in
length, it may in other cases be found to be barely one-eighth of an