66 W. BLAXLAND BENHAM. 



slavishly the exact steps of phylogeny : the mode of formation 

 of the heart in mammals^ for example, differs from that of birds, 

 nevertheless the two hearts in their entirety are surely homo- 

 logous and homogenetic; yet the ontogenetic condition cannot 

 represent a functional phylogeuetic stage. 



In the ontogeny of some Vertebrates the oesophagus 

 becomes closed at a certain period of development, and it 

 again opens out to form the permanent oesophagus. We do 

 not deny the homology (homogeuy) of these two structures. 



It appears to me that the facts which have been gathered 

 together with regard to the Affenspalte in the chimpanzee, and 

 the '' occipitalis transversus " in man, — the fact also that there 

 is considerable variation in position and extent of the fissure in 

 both animals, and that parallel variations occur in both, — are 

 so strongly in support of Ecker's view, that the mere fact of a 

 slight difference in ontogeny is not sufficient to overturn the 

 homology. 



Further, what is the course of development of the " Affen- 

 spalte " in the ape and monkey ? We are, I believe, absolutely 

 ignorant on the matter. 



In the human brain (fig. 17) it seems at first sight pretty 

 evident that the sulcus occipitalis transversus is formed by the 

 bifurcation of the intra-parietal {p*.) ; the angle formed by the 

 two branches of the fissure lends its weight to this view. But 

 compare with it fig. 18. Here p'^. gives off a branch (z.) 

 behind the arcus parieto-occipitalis, which, there is little 

 doubt, is the mesiad fork of the intraparietal, whilst the laterad 

 fork enters the transverse occipitalis. This fissure itself closely 

 resembles the "Affenspalte'' in "Sally" (fig. 11). Thus 

 Cunningham's interpretation would aj)ply to fig. 17, and 

 Ecker's to fig. 18. 



Now, in some chimpanzees, such as that represented by figs. 

 30 and 32, we have an " Afienspalte " below the operculum 

 (fig. 32) into which there falls the ramus occipitalis {p^.), 

 and at this point an angle occurs in the " Affenspalte." There 

 is, in fact, a very close resemblance to the condition in the 

 human brain (fig. 17), which Cunningham would explain as 



