REPOET ON THE SEALS. 115 



Otter in pi. vi. of his Atlas. But I find that in the brain of an Otter (Lutra vulgaris), 

 of the Badger (Meles taxus), and Batel {Mellivora indica) in the University Museum a 

 similar sunken condition of this limb of the Sylvian convolution exists. 



From the examination of these brains of Triehechus, Phoca, and Macrorhinus, I 

 am disposed to regard these animals as more or less approximating in the arrangement 

 of the convolutions of the outer face of the hemisphere to those Carnivora which 

 possess four tiers of convolutions in relation to the fissure of Sylvius. This arrangement 

 is found in the Dog, Jackal, Fox, and Wolf. 1 From Dr. Murie's figures of the brain of 

 Otaria jvbata it would appear that in that animal, whilst the Sylvian and supra- 

 sylvian convolutions are quite definite, yet that the subdivision of the marginal convolu- 

 tion of the longitudinal fissure into mediosagittal and mediolateral convolutions is so 

 partial that the arrangement seems to be intermediate to that which one finds in 

 Triehechus and the Canidad on the one hand, and the Cats on the other. In regarding 

 this affinity in the general arrangement of the convolutions of the cranial surface of 

 the hemisphere in the Seals with those of the Canidae, it must be kept in mind that in 

 the Dogs the convolutions are less tortuous, and with fewer secondary fissures and 

 gyri than in the Pinnipedia. 



The hemisphere of the cerebrum of Phoca vitulina possessed on the mesial and 

 tentorial surfaces a distinct gyrus fornicatus, or great limbic lobe, which was divided into 

 uncinate, hippocampal, and callosal convolutions, and was differentiated on its peripheral 

 side by the splenial fissure or the limbic fissure of Broca. This fissure was bridged in 

 its posterior part by a short retrolimbic gyrus, the pli de passage retrolimbique of 

 Broca. The splenial fissure had not always the same termination at its upper and 

 anterior end, for in the same brain I have seen it prolonged forwards into the crucial 

 fissure in one hemisphere, but in the other separated from it by a bridging convolution. 

 Both the suprasplenial convolution and fissure existed in the region above the corpus 

 callosum, though in one hemisphere the fissure was bridged by a short gyrus. Neither 

 the postsplenial fissure nor the splenial convolution was distinctly differentiated, and 

 the tentorial surface was subdivided into narrow convolutions. At its inferior end the 

 splenial fissure was continuous with the postrhinal fissure, and through it with the 

 transverse part of the fissure of Sylvius, across which it was prolonged into the rhinal 

 fissure, which defined the tuber olfactorium externally. The tuber was distinctly 

 prolonged into the uncinate gyrus across the bottom of the fissure of Sylvius. Imme- 

 diately to the outside of the connecting band between the tuber and uncinate gyrus 

 was the concealed portion of the anterior limb of the Sylvian convolution, which 

 apparently represented the Island of Reil. The supraorbital area possessed a gyrus 

 rectus, olfactory fissure, intraorbital fissure, internal and external supraorbital convolu- 

 tions. The olfactory peduncle was very slender, more so indeed than would be imagined 



1 St* pi iv. iii Lenret ami Gratiolet's Atlas. 



