. REPORT ON THE SEALS. 121 



interrupted by a short bridging convolution. When prolonged into a fissure it joined 

 that which lay next to the marginal convolution or the 1st curved fissure. But this was 

 not necessarily morphologically the same in all these brains. Where four tiers of con- 

 volutions were differentiated, it was, of course, the mediolateral fissure, but when only 

 three tiers were differentiated, then it probably represented the lateral fissure, as in these 

 brains both the mediolateral fissure and convolution were eithei absent or only imperfectly 

 differentiated. The coronal fissure formed the outer boundary of the sigmoid gyrus. The 

 coronal gyrus w r as the anterior part of the 2nd external convolution, which in those 

 brains that possessed four tiers of convolutions "was the mediolateral convolution ; but, 

 when only three tiers were present, it was most probably represented by the suprasylvian 

 convolution. 



The crucial fissure varied materially in its position in the genera of the Carnivora 

 and Pinnipedia. In the Seals and Walrus it was so far forward as not to be seen on 

 the dorsum of the hemispheres, but only at the anterior end of the cerebrum. In the 

 Cat and Tiger it was visible in about the anterior fourth of the dorsum of the hemi- 

 spheres ; in the Dog, Weasel, Ferret, and Coati at about the junction of the middle and 

 anterior third ; in the Badger, Polar Bear, and Ratel it was even further back, so as to be 

 just in front of a line dividing the dorsum of the hemispheres into an anterior and a 

 posterior half. This variation in the position of the fissure necessarily affected that 

 of the sigmoid gyrus which bounded it in front, behind, and on the outer side, and in 

 those brains in which the fissure was elongated and far back, this gyrus formed a well- 

 marked convolution on the dorsum of each hemisphere. When the crucial fissure was 

 elongated both it and the sigmoid gyrus were continued downwards on the outer surface 

 of the hemisphere, 1 and the direction of the coronal fissure, which formed the outer 

 boundary of the sigmoid gyrus, was from below obliquely upwards and backwards. 



It will now be of interest to compare the convolutions of the cerebrum in the Carnivora 

 and Pinnipedia with those in Man and Apes, with the view of endeavouring to ascertain 

 if any correspondence in their arrangement exists, and to what extent, in these orders of 

 Mammals. The importance of instituting this comparison has already, indeed, presented 

 itself to several anatomists, and various attempts have been made to harmonize the 

 arrangement of the convolutions of the Carnivora with those of Man and Apes. The 

 desirabdity of arriving at some definite conclusion on this matter is owing both to the 

 interest of the subject from a purely morphological point of view, and to its physiological 

 value in connection with the numerous experiments which have of late years been made 

 for the determination of the functions of the cerebral cortex. 



It wdl be obvious, if in the brains of these different orders one or two leading fissures 



1 The anterior limb of the sigmoid gyrus is sometimes called gyrus prxcruciatus (pr&frontalis), the posterior limb 

 gyrus postcruciatus {postfrontaKs). 



(ZOOL. CHALL. EXP. — PAET LXVIII. — 1888.) Yj'J' 16 



