105 
proves, that not always the same part of the brainsurface is pushed 
downwards. 
I also found out, that the ape fissure is formed when at a certain 
foetal period the occipital part of the brain begins to develop 
stronger than the preceding part, and consequently the latter is 
pushed downwards. 
According to the centre of overgrowth (greater growth) lying 
more proximally or more distally, also the line of curvation, where 
the operculisation is going to appear (ape fissure), will be placed 
more to the front or more to the back. 
It is also possible that the centre of overgrowth is placed more 
medially or either laterally. — 
This difference in localisation which influences the place of the 
curvature where the apefissure will be formed, will be of importance 
for the origin of the plis de passage. 
As I pointed out the larger growth of the occipital lobe, compared 
to the preceding part, being the cause of origin of the fissura 
simialis, of course the possibility is not excluded, that also other 
instances help to form that sulens. 
The more these instances co-operate, the more complicated the 
process will be and the more intricate the aspect of the plis de 
passage is going to be. d 
To well comprehend this, it is desirable to bring to mind in a 
few words, what has been written about the plis de passage. 
As far as I know, Grationer') has been the first that has 
treated the subject in particulars. — 
Citing ZUCKERKANDL ?), GRATIOLET makes a difference between four 
outer and two inner plis de passage. 
The first and second outer or lateral pli de passage lie in the 
fissura parieto-occipitalis and connect the lobus parietalis with the 
occipital part. The third and fourth outer or lateral plis de passage 
lie superficially and should connect the second temporal convolution 
with the occipital lobe. 
This view of Grationer dates from 1854 and therefore it 1s 
desirable, in order to prevent confusion, to add a few alterations, 
without changing however his meaning. 
For instance neither GratioLetT, nor Frarav -and JACOBSON *) 
1) GRATIOLET. Memoires sur les plis cérébrales de homme et des Primates. 
Paris 1854. 
2) ZUCKERKANDL, E. Zur Merpholcgie des Affengehirnes. Zeitschr. f. Morph. 
u. Anthr. 1903. 
8) Frarau C. u. Jacospson L. Handbuch der Anatomie des Centr. Nervensyst. 
der Säugeth. Berlin 1899. 
