REPORT ON THE SEALS. 127 



on the surface of the cortex, and to its relations to the splenial fissure on the mesial 

 aspect of the hemisphere. There can, I think, be no doubt that the anterior and upper 

 part of the splenial fissure in the brains of the Carnivora and Pinnipedia corresponds 

 with the fissure which is known as calloso-marginal in Man and Apes. Both the 

 splenial and calloso-marginal fissures are separated from the corpus callosum by the 

 callosal convolution of the limbic lobe, and each runs in this part of its course about mid- 

 way between the corpus callosum and the free upper margin of the hemisphere. In the 

 Canidse, the Badger, Eatel, Weasel, Ferret, Elephant Seal, and Walrus the splenial 

 fissure was continuous with the crucial fissure, but in the Cat, Tiger, Coati, and Polar Bear 

 they were not continuous ; whilst in a Phoca vitulina the two fissures were continuous 

 in the one hemisphere, but not in the other. In those cases in which the fissures were not 

 continuous, the splenial ended in or near the margin of the mesial longitudinal fissure 

 in proximity to the crucial fissure and usually a little behind it. 



In the human brain the calloso-marginal fissure turns round the genu of the corpus 

 callosum and then runs backwards about midway between the corpus callosum and the 

 margin of the great longitudinal fissure ; when a little in front of the splenium of the 

 corpus callosum it bends upwards to reach the margin of the hemisphere somewhat behind 

 the fissure of Bolando. Where it makes this bend a fissure is prolonged for a variable dis- 

 tance backwards from it, but does not reach the collateral fissure, for it is so interrupted 

 by convolutions in this region which are continuous with the precuneus or quadrilateral 

 lobule, that the callosal convolution loses immediately above the splenium its sharp line 

 of demarcation superiorly. Both in the human brain and that of the Ape the limbic 

 lobe, where the callosal and hippocampal convolutions approach each other, possesses a 

 less definite differentiation peripherally than is the case both in the Carnivora and in 

 Mammals generally, a condition which is apparently clue to the much greater develop- 

 ment of bridging convolutions at its splenial end. In the Walrus, for example, the 

 bridging convolution in this region (PI. IX. fig. 3) is a single narrow gyrus, whilst in 

 the human and Ape's brain they correspond to the broad base of the preecuneus. Not 

 unfrequently I have seen one or more short fissures arise from the calloso-marginal about 

 opposite the genu and indent transversely the superior frontal convolution at the anterior 

 end of the cerebrum, which was bent around each fissure like a short sigmoid gyrus. 

 In its direction and relation to the calloso-marginal fissure any one of these fissures 

 resembled the crucial fissure, but cannot be morphologically the same as the fissure of 

 Rolando, which is situated much further back on the side of the hemisphere, and which 

 has no definite relation with the calloso-marginal fissure. It is obvious that the crucial 

 fissure is not of primary importance, as it is not always present in gyrencephalous 

 Mammals, and in those Carnivora, such as the Dog and Cat, in which its development 

 has been examined, it has been shown by Pansch to appear subsequently to the splenial 

 fissure having assumed a certain depth, so that it has only a secondary value. 



