^4 Journal of Comparative Neurology. 



general considerations. 



The average canine brain, as a matter of convenience, may 

 be accepted as a simple type of a carnivore brain. The fissures 

 are clearly demarcated and there is an absence of much branch- 

 ing or secondary fissuration. 



Around the Sylvian there are three arched fissures separ- 

 ating the cortical substance into four distinct folds or gyres. In 

 the brains of cats and occasionally in dogs we find that the 

 arched fissure nearest the Sylvian is not a complete one ; that 

 only the pillars are represented, the keystone being absent. 



In Hyena and Proteles the frontal portion of this arch is 

 wanting (Krueg) but the caudal portion, fissura postica, is well 

 represented. Correlative with this state of affairs the postsuper- 

 sylvian, as compared with the presupersylvian, is situated at 

 least twice as far from the Sylvian fissure. 



In certain others of the carnivora no trace of the first arch 

 or Sylvian gyre with its its limiting fissure (anterior-postica) is 

 at all present. The first arch with its fissure has disappeared, 

 apparently swallowed up by the Sylvian. There are represented 

 then on the lateral aspect only two arched fissures, the supersyl- 

 vian and on the lateral aspect only the three gyres which they 

 separate. In those forms in which only the two arched fissures are 

 present, if the distance from the frontal portion of the super- 

 sylvian to the Sylvian be compared with the distance from the 

 latter to the postsupersylvian, it will generally be found to be 

 less in the former, and this becomes much more emphasized in 

 the case of some of the bears, where the frontal portion of an 

 undoubted supersylvian almost enters the Sylvian fissure. 



In his desciption of the brain of the Polar bear, Urstis 

 inaritimus, Turner says: "On opening up the Sylvian fissure I 

 found to my surprise that a definite arched convolution was 

 completely concealed within it. It was separated from the convo- 

 lution which bounded the Sylvian fissure by a deep fissure which 

 was also concealed. Its anterior limb, not quite so bulky as the 

 posterior, was continued into the supraorbital area immediately 

 external to the rhinal fissure and to the outer root of the olfac- 



