60 W. BLAXLAND BENHAM. 



for a considerable distance, and as such is visible also on the 

 upper surface for a greater or less extent, according as the 

 incision is deeper or shallower ; that part of the parieto-occipital 

 (= Huxley's occipito-parietal) which is seen in the upper 

 surface is the only fissure to which the term " external 

 parieto-occipital " is properly applied. 



I have shown above that this part of the parieto-occipital 

 may become separated from the so-called '' internal " parieto- 

 occipital ; but it can always be distinguished from the true 

 Alfenspalte, or Simian fissure, or subopercular furrow. 



In " Sally's " brain (figs. 10, 11) the ramus occipitalis {p^.) 

 sends off a small mediad branch {n.) in front of the parieto- 

 occipital fissure, as is very generally the case in chimpanzees, 

 the existence of which was first mentioned by Rolleston and later 

 described by Sir Wm, Turner (4). This small fissure, there- 

 fore, is of historical interest ; further, it helps to mark out 

 definitely the so-called " pli de passage superieur externe " 

 which Gratiolet claimed for chimpanzee's brain. 



The ramus occipitalis in " Sally " now curves outwards, 

 forming the outer limit of the " pli de passage " or annectant 

 gyrus or " arcus parieto-occipitalis," and enters the " Affen- 

 spalte." 



The arrangement on the two sides of the brain is not iden- 

 tical. The above description refers to the right side. 



On the left side (fig. 10) the ramus occipitalis appears to 

 bifurcate, a condition represented in some of Cunningham's 

 figures. The shorter, outer or laterad fork enters the "Affen- 

 spaltcj'^ the more conspicuous mediad fork {x.) passes back- 

 wards on to the occipital lobe in nearly a straight line. 



On the right side the ramus occipitalis also appears to bifur- 

 cate, but this is not the case. Owing to the fact that the 

 parieto-occipital fissure has become divided into two portions — 

 the "lateral" portion lying on the upper surface {lat. p. o.), 

 whilst the " internal " portion is almost confined to the mesial 

 surface and only just reaches the upper surface [mes.p. o.) — 

 the fissure [n.), which at first sight might be taken for the 

 mediad fork of the ramus occipitalis, is, as we have seen, in 



