Vice-President’s Address. 13 
associated that it is unfortunate that they should be described 
anatomically as belonging to two different lobes. The dis- 
covery by Broca of the centre for speech or phonation in 
the posterior part of the left inferior frontal convolution 
in man, and the belief that the frontal lobes are specially 
connected with the intellectual actions of cognition and 
volition, have naturally led to a very careful comparison of 
this part of the brain in man and apes. 
In 1861 the late Professor John Marshall,' in describing 
the brain of a young chimpanzee, stated that in this animal 
the dorsal end of the fissure of Rolando was situated in front 
of the transverse axis of the hemisphere, while in man it 
was to a still greater extent behind that axis. Assuming 
the length of the hemisphere to be represented by 100, the 
distance from the forepart of the brain to the dorsal end of 
the fissure of Rolando was estimated by Marshall as 47 in 
the chimpanzee and 57 in man. In a paper which I read 
before this Society in 1890, I ventured to doubt the accuracy 
of this statement, as in a brain of a chimpanzee in my posses- 
sion this fronto-Rolandic index was 61, or a little more than 
in the human subject. Professor D. J. Cunningham,’ by a 
somewhat different method of measurement, and a more 
extended series of observations, has confirmed my results. 
Thus, in the human subject, Cunningham found the mesial 
fronto-Rolandic index to be 55'3, while in the chimpanzee it 
was 55°9. The orang gave an index of 55:5, so that in these 
two anthropoids the relative antero-posterior length of the 
upper part of the frontal lobe exceeds that of man. This 
does not, however, apply to the outer part of the frontal lobe, 
as Cunningham found the outer end of the fissure of Rolando 
relatively farther forwards in the chimpanzee and orang than 
in man. In the lower apes of the Old World the whole extent 
of the fissure of Rolando is farther forwards than in man. 
Although the frontal lobe is longer near the mesial plane in 
the chimpanzee and orang than in man, yet in both these 
anthropoids it is undoubtedly narrower, the anterior part of 
1 Natural History Review, vol. i. 
2 Contribution to the Surface Anatomy of the Cerebral Hemispheres— 
Royal Irish Academy, Cunningham Memoirs, 1892, 
