. Quain's elements of anatomy . rcationof the fissare of Sylvius, into the posterior limb of which it sometimesbut very rarely opens. Its position and direction are such that thefissures of the two sides, seen from above, form a wide V-shaped figure,open in front. It is rarely interrupted in its course, appears early infoetal life (end of the fifth month), and is very uniform in man and inthe Quadrumana of the old w^orld, but is not present in mammalia gene-rally. It is apparently caused by a venous communication between thesuperior longitudinal sinus and the middle cerebral vein, which is wel
. Quain's elements of anatomy . rcationof the fissare of Sylvius, into the posterior limb of which it sometimesbut very rarely opens. Its position and direction are such that thefissures of the two sides, seen from above, form a wide V-shaped figure,open in front. It is rarely interrupted in its course, appears early infoetal life (end of the fifth month), and is very uniform in man and inthe Quadrumana of the old w^orld, but is not present in mammalia gene-rally. It is apparently caused by a venous communication between thesuperior longitudinal sinus and the middle cerebral vein, which is wellmarked in the foetus from the fom-th to the sixth month, but afterwardsbecomes atrophied (W. Krause). This furrow separates the frontal from the parietal lobe. The parallelconvolutions which bound it are named respectively the ascendingfrontal and ascending parietal convolutions. It is in the immediate neighbourhood of this sulcus that the chief of the so-called motor areas of the cerebral cortex are situated. Fig. 294. Parict. Temporo- SplieiLoidial. L. Fig. 294.—CONVOITTTIONS OP OUTER SURFACE OF RIGHT HEMISPHERE. FeOM A SIMPLT- CONTOLUTED EUROPEAN BRAIN. About half the natural size (W. R. Gowers). The convolutions are, for the most part, indicated by Roman, the furrows by italicletters. The dotted,lines indicate the divisions into lobes, the names of which are givenin full at the margin of the hemisphere. /. lio., furrow of Rolando ; jMr. -oc. f., parieto-occipital fissure ; /. Sjj. a., anterior limb, and /. Sy. p., posterior limb, of the fissure ofSylvius: , , , superior, middle, and inferior frontal convolutions; c, ascending ditto ; , ascending parietal convolution ; 1., superiorparietal lobule ; , supra-marginal convolution ; , angular convolution ; inf.,par. f., iutra-parietal furrow; , , , superior, middle, and inferioroccipital convolutions; p. n. prse-occipital notch; , ,
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