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formation of the fissura simialis therefore is, what on the other 
hand was already known, far from constant. With regard to what 
the second question to be answered is going to teach us, however, 
it is desirable to draw once more special attention to it. 
From the fact that the ape-fissure can completely develop during 
foetal life, it may indeed not be concluded, that its development, after 
birth is absolutely excluded. But when one knows, that exactly 
the same image which is found in these embryos, is also seen in 
adult specimens and when we shall demonstrate afterwards, that 
the ape-fissure develops into a period, in which the pallium has not 
by far reached its full growth and therefore is still relatively easy 
to alter, in order to form new sulci, then I feel I am right to come 
to the conclusion, that the development of the ape-fissure under normal 
circumstances, always takes place in foetal life. 
The second question, which has to be answered is: how is the 
ape-fissure formed ? 
From the embryonic brains, which 
I collected, it is proved, that for the 
first time in a semnopithecus of 13,5 
cm. by a weight of 64 er. (fig. 4) the 
formation of sulei on the occipital 
brain part is just visible. 
One sees on the lower surface, 
near the bony edge of the skull, the 
fissura Sylvii GS). which arises in an 
earlier foetal period. More caudally a 
furrow appears, demonstrable by a 
Fig. 4 slight incision (a), i.e. the suleus tempo- 
ralis superior s. paralella. 
Above the latter suleus one finds the first indication of a furrow, 
ie. a half. circular suleus (/ + ©), which continues frontally some- 
what further than the end of the fissura silvii and caudally to 
past the s. temporalis. It bends round it and continues caudally 
even rather far downwards (m). 
From what one sees in fig. 5 and 6, it may be derived that this 
half-cireular furrow, which is still very superficial, is the preliminary 
suleus interparietalis (/+e), united to the lateral part (7) of the 
sulcus parieto. occ. lateralis. 
Medially from the last part m, one finds on the brain-surface an 
incision, which is going to develop later on as the medial half (m’) 
of the s. par. occ. lat. 
