27 em. with a weight of 890 grams, the three above-mentioned 
embryos belong to the last foetal period. 
Now one sees in fig. I the suleus interparietalis (/ + e) run into 
a large crossfurrow, in which the caudal part of the arcus parieto- 
occipitalis is nearly almost submerged, whilst the incisura par. oce. 
(w) has not wholly disappeared in its depth. According to the usual 
terminology this eross-furrow (A) which contains only a part of the 
“pli de passage”, should be called an incomplete ape-fissure. 
In fig. 2 we see, that the suleus interparietalis (/ + e) runs into a 
cross-furrow (/) and that the arcus parieto-oce. has totally dis- 
appeared. The A fissure in this monkey-embryo therefore is a com- 
plete developed suleus simialis. 
Fig. 2. Fig. 3. 
Fig. 3 demonstrates a totally different aspect. Here too the sulcus 
interparietalis (J++ e) is clearly visible. In this case however it runs 
into a furrow, which also, as in fig. 2 and fig. 1 crosses the 
surface of the brain (m-m’), but in reverse of the latter, does not 
cut the edge of the mantle. It is separated by a well-developed 
gyrus. Moreover it is seen, that the incisura par. occ. med. (w) is not 
only totally visible, but also that the areus parieto-occ. (the gyrus 
around the fissure) is lying totally on the surface. 
Operculisation kas not taken place here, so that the furrow in 
which the suleus interparietalis runs is not the ape fissure, but it 
is the suleus par. oce. lat. (mm + m’). A fissura simialis does not 
appear in this embryo. 
We may therefore conclude from these three embryonic ape-brains, 
that the ape-fissure can completely develop during foetal life (fig. 2), 
but also that in other specimens its total absence can be stated. The 
