CEREBRAL CONVOLUTIONS — " SALLY." 75 



may come to be more or less entirely on the surface of the 

 hemisphere (figs. 11, 16, and 31), whilst the lower or mesial 

 portion lies on the mesial surface. This " lateral parieto-occi- 

 pital " is independent of the Affenspalte, and is not synonymous 

 with what is frequently termed in text-books the " exterual 

 parieto-occipital." 



2. The occipital operculum in the chimpanzee presents very 

 great variations in its size; the two hemispheres of a given 

 brain frequently present differences in respect of this feature 

 (cf. figs. 10, 11, 19, 20, 25, 26, 30). In ''Sally " this operculum 

 is practically absent, and the subopercular groove or " Affen- 

 spalte " is fully exposed. 



3. This " Affenspalte," or Simian fissure of the ape, seems to 

 be homologous with the "sulcus transversus occipitalis" of 

 Ecker, and to be independent of the bifurcation of the intra- 

 parietal fissure. 



4. In some chimpanzees there exists a "ramus ascendens " 

 and a "ramus horizontalis" of the anterior limb of the Sylvian 

 fissure ; these enclose a " pars triangularis " or frontal opercu- 

 lum overlapping the insula (see fig. 8). Further, I find that 

 the anterior boundary of the insula is more or less distinctly 

 marked, and that there is a distinct and sudden elevation of 

 the frontal lobe at the anterior margin of the insula. In 

 other words, an " orbital operculum " is present in some 

 chimpanzees, though it may be feebly marked in some speci- 

 mens. 



5. There is a fissure in "Sally's" brain which may possibly 

 be the homologue of the sulcus frontalis mesialis (figs. 10 and 

 11, "?/^")j though I have provisionally taken it to be a dis- 

 jointed portion of the sulcus frontalis primus, since the former 

 sulcus has not hitherto been recognised in any ape brain. 



6. Various arrangements of the frontal fissures in chim- 

 panzees resemble those recorded in man, either adult or 

 festal. 



