On tlie Viscera of a Female Chimpanzee. 301 



about equal length. According to Professor Marshall, this 

 fissure is situated farther forwards than in man. The two 

 fissures form a V, and he describes the point of the V as 

 being situated a little in front of the transverse axis of the 

 hemispheres, whilst in man it is, to a still greater extent, 

 behind that axis. Again he writes, " Suppose the whole 

 length of the hemisphere to be represented by 100, then from 

 the forepart of the brain to the point of the V w^ould measure 

 in the chimpanzee 49, and in man 57." Various other 

 authors describe and figure the fissure of Eolando as being 

 farther forwards than in man. The anterior part of the 

 cerebrum, as compared with its posterior portion, is relatively 

 narrower, and the orbital surface of the frontal lobes more 

 deeply excavated than in man. These peculiarities of the 

 chimpanzee's brain, with the forward position of the fissure 

 of Eolando, are described as combining to render the frontal 

 lobes relatively much smaller than in the human subject. 

 Indeed, Marshall, in his paper already referred to, considers 

 that "whereas nearly one-half of the upper surface of the 

 cerebrum lies in front of the fissure of Eolando in man, a very 

 little more than one-third is so placed in the chimpanzee" 

 (p. 36). I have examined my own specimen, and find that it 

 supports Marshall's views in respect of the diminished 

 breadth and depth of the frontal lobes, but not with regard 

 to its length as determined by the position of the fissure of 

 Eolando. Of course, in measuring the position of this fissure 

 in relation to the anterior and posterior extremities of the 

 brain, it is necessary to decide how the brain is to be held. 

 In my case the brain was kept in the cranial cavity, and the 

 skull so placed that the orbits looked forwards. The position 

 ot the head nearly corresponded with that of the chimpanzee 

 shown in mesial section in Plates 7 and 8 of Professor 

 Cunninofham's work.^ 



rio\ 1 is a life-sized drawing^ of a vertical mesial section of 

 my chimpanzee's brain. It shows the position in which it 

 was placed in estimating the position of the fissure of Eolando. 

 The X indicates the situation of the upper end of the fissure 

 in relation to the anterior and posterior extremities of the 



^ Royal Irish Academy — " Cunningham Memoirs," No 2, 1SS6. 



