1892.] CEREBRAL HEMISPHERES OF RODENTS. 611 



these furrows are, however, deeper than in Dasyprocfa. The cliief 

 point of agreement between them, and that which causes them to differ 

 from the two remaining families, is the absence of the Sylvian fissure; 

 this brings Hydrochcerus into relation rather with the Dasyproctidge 

 than the Caviidae, where it is placed by Alston. Judging also from 

 Dareste's figure, the general outHne of the brain of Hydrochosrus is 

 like that of Ccelogenys, but also of Lagostomus. In all these three 

 genera the principal longitudinal fissure, which I have called " a," 

 is divided into two portions, one anterior and one posterior. Apart 



Fiff. 6. 



Brain of Aulaeodus, viewed from above. 

 8y, Sylvian fissure ; a, longitudinal furrow. 



from this the brain of Lagostomus appears to be nearer to that of 

 DoUchotis. They have botla of them a deep Sylvian fissure, and the 

 furrows b and c tend to converge towards the middle line ; finally, 

 the rhinal fissure in both genera is deeper behind than in front. I 

 have not ventured to treat at length of the evidences of affinity 

 afforded by the convolutions, since the illustrations are before the 

 reader, who can form his own opinions. 



List of Papers and BooTcs referred to. 



(1) Dareste, C. — " Note sur le Cerveau des Rongeurs et particu- 



lierement sur le Cerveau du Cabiai," Ann. Sci. Nat. ser. 4, 

 vol. iii. (1855), p. 3.55, pi. xi. 



(2) Turner, Sir W. — "The Convolutions of the Brain: A Study 



in Comparative Anatomy," J. Anat. Phys. vol. xxv. pp. 105 

 -153 (1891). 

 (Z) Beddard, F. E. — " Notes on the Anatomy of DoUchotis 

 patagonica," P. Z. S. 1891, p. 236. 



(4) Beddard, F. E. — " On the Brain and Muscular Anatomy of 



Aulaeodus," P. Z. S. 1892, p. 520. 



(5) MivART, St. George. — "Notes on the Anatomy of Erithizon 



dorsatus," P. Z. S. 1882, p. 271. 



