The convolutions of the brain : a study in comparative anatomy : being an address delivered to the Anatomical Section of the Tenth International Medical Congress in Berlin, August 5, 1890 / by Sir William Turner.

  • William Turner
Date:
1890
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Licence: Public Domain Mark

Credit: The convolutions of the brain : a study in comparative anatomy : being an address delivered to the Anatomical Section of the Tenth International Medical Congress in Berlin, August 5, 1890 / by Sir William Turner. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    may be called sagittal or marginal (m), for it forms the margin of the great mesial fissure. This fissure is, as previously stated occasionally present in the brains of rodents and bats and appears indeed in the pallium of these and some other mammals before there is any definite evidence of a Sylvian fissure. In the study of the Sylvian fissure care should be taken to discriminate between it and the Sylvian fossa or vallecula As already pointed out, the Sylvian fossa (v) is a depression in the rhinencephalon immediately in front of the lobus hippocampi, and It is seen as low down as the brains of the monotremes. The Sylvian fissure, on the other hand, belongs to the pallium. It is not seen in the smooth-brained Omithorhynchus, or in the^ hssencephalous rodents, insectivores, or bats. In Echidna, again, the small fissure, marked s in fig. 9, may perhaps represent ^ a Sylvian fissure. In Macropus major I think it is^ possible that the middle vertical transverse fissure is a Sylvian ^ fissure. The radiating character ot these fissures in the brains of Macropus and Halmatmws, in which it must be remembered the corpus callosum is rudimentary, is of interest in connection with the radiated arrangement of the transitory fissures on the cranial surface of the human brain at an early stage of development.^ In Hyrax the more anterior vertical transverse fissure is also perhaps to be regarded as representing a Sylvian fissure, though it does not reach the rhinal fissure. It would appear, therefore, that in the evolution- of the brain in the mammalian series the Sylvian fissure may be present in the brains of such low mammals as Bchidna and Macro2ms, which are also convoluted, whilst it is absent in the smooth-brained rodents, bats, and insectivores—mammals that in other respects are more highly organised than the mono- tremes and marsupials. Further, in these lissencephala there is a tendency for a sagittal fissure and a marginal convolution to differentiate on the cranial surface before there is any evidence of a Sylvian fissure being present. But the mesial surface of the pallium is also of interest in connection with the appearance in it of fissures and convolutions. ^ See an interesting discussion on these complete fissures in tbe human brain by Professor D. J, Cunningham in Journal 'of Anatomij and Physiology, April 1890.
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