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Show 606 MR. F. E. BEDDARD ON THE [Dec. 6, able to examine leads me to disagree with some of the statements in Dareste's paper (1). After describing the convolutions of the Capybara he remarks :-"II n'existe point dans les autres Rongeurs de veritables circonvolutions ; mais les anfractuosites et les depressions que Ton observe a la surface du cerveau de leurs grandes especes sont manifestement, dans leur disposition, 1'ebauche et comme l'indication des circonvolutions si developpees et si nettement des-sinees du Cabiai." Sir William Turner also, in his interesting survey of the Mammalian brain (2), says upon the same subject :-- "The Rodentia are almost universally smooth-brained. But in some genera traces of shallow fissures may occasionally be seen on the surface which indicate an early stage in the formation of convolutions." It appears to me that both these statements underestimate the actual development of fissures and convolutions * upon the brain of the larger Rodents. I do not, I confess, see any reason for M . Dareste's distinction between the " circonvolutions " of the brain of Hydrochcerus and the " anfractuosites " of the brains of some other forms; perhaps, however, Dareste had not in his hands such well-preserved brains as I have been able, thanks to the skill of m y assistant Mr. Ockenden, to examine. Judging from a specimen of the brain of Hydrochcerus which I have seen by the kindness of Mr. Charles Stewart in the Museum of the Royal College of Surgeons, the fissures in this rodent are not more marked than they are in, for example, Lagostomus ; but the latter is one of the best developed brains in this respect, and it is one of the types which M . Dareste did not examine or refer to; I should, however, dispute his statement even when applied to the Agouti; I think that a comparison of m y figure of the brain of this rodent with M. Dareste's figures of the brain of Hydrochcerus will bear out my remarks. Another point in which I find myself in disagreement with M. Dareste concerns the Sylvian fissure. H e remarks, and judging from his figure with perfect truth, that the Capybara has no fissure in its brain which can be compared to this universally present fissure ; it is, however, a little rash to found upon the examination of a single type (he says nothing in this matter of the other Rodents' brains) a generalization of so much importance as that which Dareste proceeds to formulate, viz.:-" Le cerveau des Rongeurs nous presente, selon toute apparence, un type distinct de celui des Primates, des Carnivores et des Ruminants ; type principalement caracterisee par l'absence de la scissure de Sylvius, et par suite par l'absence de la division du cerveau des deux lobes, l'un anterieur, l'autre posterieur a la scissure." Sir W . Turner also remarks that "The Sylvian fissure ... is not seen ... in the lissencephalous Rodents." The Sylvian fissure is undoubtedly feebly developed in the majority of those Rodents 2 the brains of which I have personally 1 Leuret and Gratiolet head plate iii., on which Rodents' brains are figured, with tbe title " Encephale des Mammiferes dont les lobes cerebraux sont depourvus de circonvolutions." 3 The Sylvian fissure also exists in a few perfectly smooth-brained Eodents for instance in the following:-Sciurus, Bipus, Gerbillus, Chinchilla. |