CEKEBEAL CONVOLUTIONS — " SALLY." 65 



Professor Lankester very generously gave me permission to 

 dissect one of them to ascertain what was the fact with regard 

 to this point. I sliced the hemisphere in planes parallel to the 

 median plane till I cut through the posterior cornu of the lateral 

 ventricle. I find that the " Aflfenspalte " does not cause a 

 bulging in the roof or side of the ventricle. In the figure (fig. 9) 

 there appears to be such a bulging, but this is a portion of the 

 * calcar avis ' passing on the roof of the ventricle, and the slight 

 ridge {cc)j ust in front of it lies distinctly in front of the Affenspalte. 

 Miiller, who represents dissections of the brain of a chimpanzee, 

 does not figure or describe any such bulging. But even if there 

 were such an elevation of the outer wall of the ventricle in the 

 lower apes, it does not seem to me a consequence that the higher 

 apes would present one. Even if in the ordinary chimpanzee 

 with a well-marked operculum and deep Afi'enspalte the impress 

 of the latter is exhibited by the outer wall of the ventricle, it does 

 not necessarily follow that in the condition in which the Affen- 

 spalte is present in " Sally,"" the same impress would be left. 



As the operculum disappears, and the Affenspalte becomes 

 proportionately shallower, it seems quite possible that the 

 bulging of the ventricular wall should get less and less 

 marked. 



In the human brain the " occipitalis trausversus,'' as we 

 have seen, replaces the " fissura perpendicularis externa ^' after 

 the disappearance of all trace of the latter. It does not how- 

 ever follow, because there is no actual continuity of the two 

 grooves, that there is no genetic relation between them. The 

 obliteration of the earlier furrow is probably due to the growth 

 of the nerve tissue bringing about a thickening in the wall of 

 the ventricle, and " filling up " (if we may use the expression) 

 the furrow ; at the same time the bulging on the inner face 

 becomes smoothed out. But the furrow again makes an effort 

 — inheritance is too strong for the vegetative growth, — and 

 succeeds in obtaining its permanent position as the " occipitalis 

 trausversus," which is relatively shallower and does not cause 

 any bulging inwards of the wall of the ventricle. 



We know that ontogeny does not by any means follow 



VOL. 37, PART 1. — NEW S£R. B 



