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depth in 8 than in fig. 7. The ape-fissure which is more developed, 
therefore, as is shown, does not run along the whole of the 
suleus parieto-oce. lat. (m + m’), but it continues along m, further 
along that part of the arcus par. oee. (o) which is pushed downwards, 
and along the incisura par. oee. towards the medial face of the brain. 
A further period of development, which I will demonstrate more 
conveniently on a newly born monkey, fig. 9 (length 27 cm. weight 
330 er), teaches us what follows: 
On the right hemisphere, where the two walls have been drawn 
aside, we see in the depth, that in the posterior part of the arcus 
parieto-oce., i.e. the pli de passage, a change has begun, because it 
is, as it were, divided into two portions, each part respectively 
marked by + and o. 
Fig. 9. 
Between them one sees a dark small furrow, which on further 
opening of the ape-fissure, proves to be nothing else than a deep 
curvature. Moreover the m + m’ sulcus, which is totally removed to 
the bottom is invisible. Whilst we can still see it on fig. 8, lying 
on the posterior lip of the ape-fissure, it is now totally pushed to 
the bottom of the sulcus on fig. 9. 
Fig. 10, taken from an adult macacus cynomolgus, shows us a 
distinct aspect of a well-developed ape-fissure. On the right one 
clearly sees this suleus passing from the medial to the lateral surface. 
On the left the operculum is excised and one looks upon the front 
face of the ape-fissure. The incisura par. oce. (w) runs obviously in 
the ape-fissure. The sulcus interparietalis (/ + e) on the parietal sur- 
face too continues in the anterior part of the ape-tissure. The mm’ 
