939 
The development of the rims above the fossa Sylvii, which lies 
a little lower, progresses in the 5% month. 
A distinct separation between an anterior and a posterior part of 
this suleus one gets in the following, therefore in the sixth month. 
Now too this fossa is nearly totally open, only the posterior part 
has closed to a fissure. 
During the following months the process of operculisation con- 
tinues, so that in the 9'* month only the most inferior part is still 
opened. 
Rerzius ') gives in his treatise firstly an account of the description, 
made by CUNNINGHAM, who states that the fissura lateralis begins as 
an almost round furrow, which later on becomes a triangle. Rerzius 
himself describes its appearance in the middle of the 3'¢ month 
in the shape of a half-moon or kidney, also as a sharp point. 
(Pl. I fig. 28—29). At first however one does not notice much of 
an insula. In the beginning of the 5** month the marked area 
becomes broader. 
Although from the above-mentioned may follow, that the form in 
which the fossa Sylvii begins is not always the same, yet on one 
point agreement exists, that is to say, this furrow begins at the 
lateral edge and from the very first commencement is opened 
towards the lower end. 
Limiting myself, in reference to the foetal brains of anthropoids, 
to the investigations of the latest periods, therefore those of ANTHONY *), 
I may state he then found in a foetus of a gorilla of 6—8 months: 
“Le circulair superieur de Reil s'étend, au côté gauche, comme chez 
un foetus humain du même age, jusqu'au sillon limite gntérieur de 
insula... A droite le circulaire superieur de Reil est conforme au 
type habituel observé chez les singes, c'est-à-dire, qu'il n’atteint pas 
le sillon limite antérieur de Vinsula’. 
As to the foetal brains of a chimpanzee ®), corresponding with 
human brains of the 7 and 8t* foetal month, these should differ 
with regard to the “complex Sylvin”. For this communication, 
however, it is of importance that this furrow in this period is already 
totally closed. 
In embryos of Semnopitheci the relation is quite different from that 
in human beings. 
1) D. Rerztus. Das Menschenhirn. Stokholm 1896. 
2) ANTHONY, R. Sur un cerveau de foetus de gorille. Comptes rendus des séances 
de l'Académie des Sciences, t. 161, p 153 séance du 9 Aout 1915, Paris. 
3) Id. Sur un cerveau de foetus de chimpansé. Comptes rendus des séances enz 
t. 162, p. 604, séance 17 Avr. 1916, Paris. k 
60% 
