1580 
enlargement of the occipital part, then the nomenclature of incom- 
plete and complete ape-fissure is of course irrational, as the ape- 
fissure itself, in that case, is totally secondary, depending on the 
enlargement of the occipital lobe. It is however advantageous 
to keep to these names, if one wants to point out whether a smaller 
or a larger part of the first pli de passage is pushed downwards. 
But one should be- aware of the fact that the cause of the ape- 
fissure bas to be lookedf or in an enlarged growth of the occipital lobe. 
I repeat here onee more with emphasis, that if the development 
of the parietal and occipital lobes takes place regularly, there is no 
question of the formation of the ape-fissure. For that reason, although 
it is often done, the fissura simialis can never be compared with 
the fissura sylvii. The latter, it must be said, develops secondarily, 
but the formation of the insula is a normal thing. The fissura sylvit 
therefore belongs to the constant sulci, while the ape-fissure has to 
be reckoned to the inconstant ones. 
Further it is distinetly proved by the different periods of develop- 
ment, that a primary cavity as is supposed by Koniprucer, which 
is secondarily opereulized by the surrounding matter cannot be ex- 
pected. Just the reverse has to be expected, that is to say, oper- 
culisation as a primary process, the ape-fissure as the result of it, 
therefore secondarily formed. 
The third question, which | have put to myself, is this: where, 
on which spot, is the ape-fissure formed? 
This question is of importance, because several investigators in 
their description of the fissura simialis, have always tried to prove 
its existence, e.g. through its place in regard to the other sulei. It 
is therefore of much importance to see whether this place is so 
constant, that it may be expected as a proof, that a certain sulcus 
is the ape-fissure, or not. 
We shall see, that this view is only partly See and has given 
rise to a great number of mistakes. 
When I in first instance take the semnopitheci, then we know 
that the occipital part is separated from the parietal by a cross- 
furrow, the suleus par. oce. lat. me Jm’ (fig. 6 and 7). 
If the lobus occipitalis develops very strongly and tries to oper- 
culize the preceding part, then it is natural. that it takes place in 
the neighbourhood of the 7 + m’ suleus. The surface of the brain 
has there, through this suleus, a cross furrow and therefore on that 
spot becomes a locus minoris resistentiae, and thus it is predisposed 
to be bent in and to be pushed downwards. 
