126 THE VOYAGE OF H.M.S. CHALLENGER. 



that stimulation of the area marked (16) on the lower end of the anterior limb of the 

 Sylvian convolution in Dr. Ferrier's figures of the brain of the Dog and Cat is occasionally 

 associated with movements of the lips, whilst similar movements are produced by irrita- 

 tion inside the fissure of Sylvius in the Monkey, 1 doubtless due therefore to irritation of 

 the areas (9) and (10) which lie in proximity to the fissure. 



To harmonize the arrangement of the convolutions of the frontal, parietal, and 

 occipital lobes of the human and Ape's brain with the tiers of convolutions which in the 

 Carnivora surmount the fissure of Sylvius, is undoubtedly a task of some difficulty. 

 Several anatomists have, however, attempted to do so. M. Broca, in his memoir already 

 quoted, has argued with great emphasis, that in the brain of the Primates the character 

 which dominates over all others in importance is the enormous development of the 

 frontal lobe, from whence results the backward position and the obbque direction of the 

 fissure of Rolando. The position which I took up many years ago 2 that the fissure of 

 Rolando, or central fissure, should be regarded as forming the posterior limit of the frontal 

 lobe and the plane of demarcation between it and the parietal lobe, is now generally 

 accepted. It becomes therefore a matter of some moment to determine if possible the 

 fissure in the carnivorous brain which corresponds to the fissure of Rolando in Man and 

 Apes, the oblique and backward direction of which must be borne in mind. 



Broca regarded the fissure of Rolando as represented in the Carnivora by the prae- 

 sylvian fissure, so that he practically confined the frontal lobe in these animals to the 

 region in front of and below that fissure, which has been named in this Report the supra- 

 orbital area. Schwalbe is apparently inclined to attach some weight to this view ; but 

 owing to the divergence in development of the Carnivora and Ungulata on the one hand, 

 and the Primates on the other, he does not consider it possible to make a strict comparison 

 between the convolutions and furrows of these orders of Mammals. I believe that the 

 limitation of the frontal lobe to the area in front of the prsesylvian fissure would be too 

 great a restriction of that lobe, which on developmental and other grounds may, I think, 

 be shown to extend further back in the hemisphere. 



At the first glance there might seem to be a strong likeness between the crucial 

 fissure in the carnivorous brain and the fissure of Rolando. They are both directed more 

 or less vertically and transversely downwards on the cranial surface of the hemisphere, and 

 each is bounded in front and behind by a gyrus having a corresponding direction ; in the 

 Carnivora the gyri are the anterior and posterior limbs of the sigmoid gyrus ; in Man and 

 Apes they are the ascending frontal and parietal convolutions. These general resemblances 

 have led more than one anatomist to regard them as homologous. But in discussing the 

 homology of the crucial fissure it is important to attend to its relative period of ajjpearance 



1 I am indebted to Dr. Ferrier for this information, which he wrote to me in reply to a request as to the area in the 

 Monkey's brain which corresponds to (16) in the brain of the Dog. 



2 The Convolutions of the Human Cerebrum topographically considered, Edinburgh, 1866, p. 11. Notes more 

 especially on the Bridging Convolutions in the Brain of the Chimpanzee, Proc. Roy. Soc. Edin., 19th Feb. 1866, vol. v. p. 578. 



