1892.] CEREBRAL HEMISPHERES OF RODENTS. 611 



these furrows are, however, deeper than in Dasyprocta. The chief 

 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 Hydroehoerus into relation rather with the Dasvproctidae 

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

 Dareste's figure, the general outline of the brain of Hydrochoerus 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 j)ortions, one anterior and one posterior. Apart 



Fig. 6. 



Bi-ain of Aulacodus, viewed from above. 

 Sy, Sylvian fissure ; a, longitudinal furrow. 



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

 BoUchotis. They have both 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 Books referred to. 



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



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

 vol. iii. (1855), p. 355, pi. xi. 



(2) TuRNKR, 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 BoUchotis 

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



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



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



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



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



