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Show 1899.] BRAIN OF HYDROCHCERUS. 799 The rhinal fissure separating the hemispheres from the underlying 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 Hydrochcerus, 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 hippocampal lobe which are thus described:-" E n dedans de cette circonvolution est un sillon qui delimite le petit appareil des corps stries et des couches optiques qui est ici tres developpe." I find these structures to be shown with great clearness in the brain now before m e (fig. 2, a). They are, however, rather longer in form than they are figured by the authority from w h o m I have just quoted. Nor have they, as erroneously 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). |