1899.] 



BEAIN OF HYDEOCIKERXTS. 



799 



The rhinal fissure separating the hemispheres from the uuderlyiug 

 pallium is very strongly marked. It does not quite reach the 

 anterior end of the brain, so that here the pallium seems to bend 

 down and become perfectly continuous with the underlying lobe. 



Fig. 1. 



Brain of Hydrochoerus, dorsal view. Nat. size. 



a, internal longitudinal fissure ; b, middle ditto ; c, external ditto ; d, crucial 

 fissure (?) ; s, Sylvian fissure. 



Dareste draws attention to two structures on the ventral side of 

 the hippocanipal lobe which are thus described : — " En dedans de 

 cette circouvolution est un sillon qui delimite le petit appareil des 

 corps strics et des couches optiques qui est ici tres developpe." 

 I find these structures to be shown with great clearness in the 

 brain now before me (fig. 2, a). They are, however, rather longer 

 in form than thej'^ are figured by the authority from whom I have 

 just quoted. Nor have they, as erroneous!}' represented in the 

 figure of Dareste, anything whatever to do with the origin of the 

 optic nerves. The latter can be plainly seen to dip down over the 

 outer side of the crura cerebri. On the other hand, one of the 

 principal roots of the olfactory nerve does arise from this delimited 

 area of brain -tissue, a fact which is not figured or referred to by 

 Dareste. This point should be perfectly clear from the drawing 

 exhibited (fig. 2). 



