204 PROCEEDINGS OF THE ACADEMY OF [1892. 



The brain, that of a young Gorilla, weighed one hundred and fifty 

 grammes and measured ninety millimetres in length, seventy-five mil- 

 limetres in breadth and sixty millimetres in height and was somewhat 

 smaller than either of the brains previously described by Pansch and 

 Bfoca. Each hemisphere of the cerebrum of the Gorilla, like that 

 of man, is incompletely divided by more or less well defined and deep 

 fissures into the following five divisions or lobes, viz: the frontal, 

 parietal, occipital, temporal, and central lobes. The fissure of Sylv- 

 ius, PL XI, fig. 2 S, begins at the base of the hemisphere behind the 

 origin of the olfactory nerves, and laterally from the optic chiasma. 

 Passing thence outwardly it reaches the arched lateral surface of the 

 hemisphere and divides into two branches. The posterior branch, PI. 

 XI, fig. 2 S', the longest of the two passing obliquely upward and back- 

 ward terminates in the supra-marginal convolution of the parietal 

 lobe. The anterior vertical branch, PI. XI, fig. 2 S", the smallest of 

 the two into which the Sylvian fissure divides, passing obliquely for- 

 ward and then upward and slightly backward, terminates in that 

 part of the third frontal convolution which is situated below the 

 second frontal fissure and in front of the pre-central fissure. The 

 anterior horizontal branch, the third into which the Sylvian fissure 

 divides in the brain of Man, and usually undescribed even in special 

 works upon the brain, while absent in this specimen appears to have 

 been present in the brain of the Gorilla described by Broca. It 

 should be mentioned in this connection, that this fissure, regarded by 

 Broca as being the anterior horizontal branch of the fissure of 

 Sylvius, was described by Pansch as the anterior vertical branch, 

 and by BischofT as the orbital branch, both BischoflP and Broca 

 regarding the slight indentati(>n above but not passing into the pos- 

 terior branch of the Sylvian fissure, as the ascending vertical branch. 

 Such an indentation is present, at least in the right hemisphere of 

 the brain of the Gorilla under consideration, but we cannot attach to 

 it the morphological significance attributed to it. 



The difference in interpretation of this fissure may be due to 

 the fact of the brains described by Bischoff and Broca diflfering from 

 each other and from that now described. Within the angle formed 

 by the anterior and posterior branches of the Sylvian fissure may be 

 seen, on the right side at least, of the brain of our Gorilla, the fifth 

 lobe or island of Reil, the operculum leaving it partly uncovered. 

 On the left side of the brain, however, the operculum fits so closely 

 into the angle just referred to, that the island of Reil is completely 



