REPORT ON THE SEALS. 129 



stimulus. These experiments all indicate a homology between both limbs of the sigmoid 

 gyrus in the Dog and the ascending, superior, and middle frontal convolutions in the 

 Monkey, which is incompatible with the view that the crucial fissure is the homologue of 

 the fissure of Eolando, but quite reconcdable with the theory that the coronal fissure 

 and fissure of Rolando are homologous ; for in the respective 1 trains both the coronal and 

 Eolando's fissures lie behind the areas stimulated, with the exception of a small part 

 of (4), which just touches the ascending parietal convolution. 



On the other hand, it is more difficult to reconcile some other of Ferrier's experiments 

 with this conclusion as to the homology of the two fissures. For stimulation of area (1), 

 placed in the Monkey in the postero -parietal convolution just in front of the parieto- 

 occipital fissure, and in the Dog in the posterior limb of the sigmoid gyrus just behind the 

 crucial fissure, produced in both animals an advancement of the opposite hind limb as in 

 walking ; in the Monkey the area stimulated was distinctly behind the fissure of Rolando, 

 in the Dog well in front of the coronal fissure. Again, the areas (7) (8), which when 

 stimulated gave rise to movements of the zygomatic muscles and upper lip, he in the 

 Monkey in the ascending frontal convolution, and therefore anterior to the fissure of 

 Rolando ; but in the Dog the one is situated in the coronal part of the 2nd external 

 convolution, the other in the anterior composite convolution formed by the junction of 

 the anterior ends of the 2nd and 3rd external convolutions, and both therefore are behind 

 the coronal fissure. 



If we regard, however, the whole evidence based on comparative anatomy, on the 

 depth and relative time of appearance of the fissures and on the results obtained by 

 stimulating the brain in front of the fissures, we may, I think, fairly assume the 

 fissure of Rolando to be homologous with the coronal fissure in the carnivorous brain. 

 The sigmoid gyrus with the adjoining part of the sagittal convolution, and in animals 

 which have an ursine lozenge that area also, would therefore represent the superior, 

 middle, and ascending frontal convolutions in the brain of Man and Apes. 



But there are other fissures in the brains of these Mammals the homologies of which 

 it is desirable, if possible, to determine. A well-marked fissure in the carnivorous brain 

 is the praesylvian or supraorbital fissure. It is the most anterior of the three primary 

 fissures described by Pansch as appearing on the cranial surface of the brain of the fcetal 

 Dog, and it separates in this animal the anterior limbs of the four tiers of convolutions 

 from the supraorbital area and the prorean convolution. If we place side by side the 

 hemispheres of the Human and the Dog's brain we can see in the former two fissures, the 

 prsecentral fissure of Ecker and the ascending branch of the Sylvian fissure, one or other of 

 which would appear to represent the prassylvian fissure in the Dog. Meynert was of opinion 

 that the praesylvian fissure is homologous with the ascending branch of the Sylvian fissure. 

 Broca objected to this * on the ground that the ascending branch, whilst present in Man 



1 Sur le cerveau du Gorille, Revue d 'Anthropologic, s£r. 2, t. i. 

 (ZOOL. CHALL. EXP. — PART LXVIII. — 1888.) - Yyy 17 



