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220

Cunningham Memoirs.

But again, in my examination of the adult human brain, I have not
found the ramus occipitalis completely cut off from the ramus horizontals
in so large a percentage of cases as Professor Wilder. I have examined
133 hemispheres with the view of determining the relative frequency
of this confluence of the ramus occipitalis and ramus horizontalis. The
following are the results I obtained:—

Relativk frequency of the Confluence of the Ramus Occipitalis with

the Ea us Horizontalis.

Number of Hemispheres Examined and
Period of Development.

The two Sulci Continuous.

The two Sulci separated by
a Superficial Gyrus.

Actual
Number of
Hemispheres.

Percentage.

Actual
Number of
Hemispheres.

Percentage.

77 (adult), .....

49

63-7

28

36-3

16 (children from 3 mths. to 12 yrs.),

10

62-5

6

37-5

19 (full-time foetuses), .

11

58-8

8

42-2

21 (eighth-mouth foetuses),

7

333

14

66-7

From this Table it is evident that in many cases the union of the two
fissural elements is delayed until after birth. In the adult, however, the
confluence had not taken place at all in 36-3 per cent, of the hemispheres
examined.

I can confirm in every particular a statement which has been made both
by Ecker and Wilder, viz. that the union of the ramus occipitalis and the
ramus horizontalis of the intraparietal sulcus takes place more frequently
on the left side than on the right side. In 28 hemispheres which I studied
in connexion with this question I was much surprised to find a union of the
two elements in 87*5 per cent, of the left hemispheres, and in only 584 of
the right hemispheres.

VI. The Sulcus Occipitalis Transversus of Ecker.—The question we
have now to decide is whether the sulcus occipitalis transversus is to be