84 W. BLAXLAND BENHAM. 



Tig. 23.— The hinder portion of the same brain (947/.), with the operculum 

 turned back and the " AfiFenspalte " exposed. The intraparietal fissure 

 {I. P.) enters the parieto-occipital {JaL p. o.), which is separated from tl)e 

 Affenspalte by a large gyrus — a part of the arcus. The shaded parts indicate 

 those which are concealed by the operculum in Fig. 24. 



Fig. 24. — The mesial surface of the hinder part of the same hemisphere 

 (947/.), to further illustrate the relations of the parieto-occipital fissure. In 

 this instance this fissure does not meet the calcarine. 



Fig. 25.— A tracing of the chimpanzee's brain figured and described by 

 Miiller. 



Fig. 26. — The hinder part of the right hemisphere of a chimpanzee (Oxford 

 Museum, 947 i.). The operculum is intermediate, as regards the size and 

 development, between the usual condition and that of " Sally ;" the " Affen- 

 spalte " is, however, concealed. The " lateral parieto-occipital " {lat. p. o.) 

 is separated from the mesial parieto-occipital {mes. p. o.) by the gyrus inter- 

 cuneatus («.). 



Fig. 27. — The mesial surface of the same brain (947 i.),io further illustrate 

 the condition of the parieto-occipital fissure. The shaded parr, is the under 

 surface of the occipital lobe. b. c. y. are three branches of the mesial portion 

 of the parieto-occipital. a. The gyrus intercuneatus. This figure also shows 

 the distinction of the affenspalte from the parieto-occipital fissure. Note 

 that the calcarine and parieto-occipital fissures meet. 



Fig. 28. — Projection view of the dorsal and lateral surfaces of the left 

 frontal lobe of the chimpanzee exhibited in the Court (Oxford Museum, 

 No. 910). 



Fig. 29. — The mesial surface of the hinder part of the right hemisphere of 

 a chimpanzee's brain (exhibited in the Oxford Museum, No. 910), to illustrate 

 the arrangement of the parieto-occipital fissure, which does not join the 

 calcarine. The shaded portion indicates the lower surface of the occipital lobe. 

 Figs. 30—34 illustrate the brain of a chimpanzee (Oxford Museum, No. 

 947 «.). Natural size. 



Fig. 30. Dorsal view. It illustrates two stages in the diminution of the 

 operculum. On the right side a condition very similar to that of 

 " Sally" is seen on turning back the small operculum, as in Fig. 32. 

 On the left the operculum is larger, and the condition of the fissures 

 somewhat peculiar. 

 Fig. 31. The hinder part of the left hemisphere, with operculum turned 

 back. The shaded parts indicate the portions ordinarily concealed by 

 that structure. The parieto-occipital, which is undivided, passes for a 

 considerable distance over the surface of the hemisphere. The Affen- 

 spalte is divided into two pieces, the outer of which receives the intra- 



