RETORT ON THE SEALS. 95 



into convolutions by certain fissures. The most obvious of these sulci was the olfactory 

 fissure (ol), in which the slender olfactory peduncle was lodged, and which was situated 

 parallel to the mesial longitudinal fissure. Between and parallel to the olfactory and 

 longitudinal fissures was the gyrus rectus (re), which extended from the locus perforatus 

 anticus forward to the prorean convolution at the anterior end of the hemisphere. The 

 rhinal fissure (rh) (Wilder), 1 formed the outer boundary of the tuber olfactorium ; it was 

 shallow and was prolonged forwards into the olfactory fissure and backwards into the 

 Sylvian fissure. External to the tuber olfactorium and the olfactory peduncle was an 

 intraorbital fissure 2 (io) closely resembling what I have described in the brain of Man and 

 the Chimpanzee as the triradiate fissure? Its radiations by breaking up the supra- 

 orbital area contributed materially to the convoluted character of this part of the brain. 

 Between it and the olfactory sulcus was a convolution which I shall name internal 

 supraorbital (isc), and between it and the praesylvian fissure was a convolution which may 

 appropriately be named external supraorbital (esc). 



Returning again to the crucial fissure, at the spot where it changed from the 

 oblique to the transverse, a short sulcus (fissura prsecruciata, pc, Krueg) proceeded 

 forwards and inwards from it, which along with the crucial and mesial longitudinal 

 fissures marked off a convolution 27 mm. long, and as this arrangement occurred in both 

 hemispheres a lozenge-shaped area was produced. This area was first noticed by St. 

 George Mivart in the brain of the Arctoid Carnivora, and was named by him Ursine 

 lozenge. In the Elephant Seal, as Mivart has also described in Phoca vitulina, this 

 lozenge could not properly be seen until the hemispheres were slightly separated from 

 each other (ur). It is of small size as compared with the corresponding area in the 

 brain of Ursus maritimus. The prorean convolution {pre) was 17 mm. long ; it was 

 bounded externally by the prorean fissure, and internally by the mesial longitudinal 

 fissure ; it was immediately above the gyrus rectus, whilst the ursine lozenge was placed 

 above and to its inner side. 



The convolutions which lie around the Sylvian fissure were much more complex in 

 arrangement than in the brains of the Dogs, Cats, and Bears, which was due in the 

 Elephant Seal to their greater tortuosity and the more numerous secondary sulci. 



Owing to the various modes of nomenclature which have been adopted by different 

 anatomists in describing the tiers of convolutions which surmount the Sylvian fissure, 

 the selection of the names to be applied to them in this description has been difficult. 

 Leuret, in those brains where the tiers were four in number, simply distinguished them 

 by numbers — I, II, III, IV — in their order from below upwards from the Sylvian to the 

 mesial longitudinal fissure. Broca also named them from below upwards the 1st, 2nd, 



1 Ecto-rhinal, Owen. 



- Intraorbital fissure of the carnivorous brain, Flower and Langley. 



3 The convolutions of the Human Cerebrum topographically considered, Edinburgh, 1866. Notes more especially 

 on the Bridging Convolutions in the Brain of the Chimpanzee, Proc. Boy. Soc. Edin., February 19, 1866, vol. v. p. 578. 



