672 GENERAL REAIARKS 



the lower parts of the frontal lobes whicli receive supplies of blood 

 from the anterior cerebral as well as from the middle cerebral 

 arteries; the deep fissure of Rolando, though the convolutions 

 bounding- it may not be quite so advantageously supplied as the 

 horizontal convolutions just spoken of, has nevertheless a double 

 supply both from the middle and from the anterior cerebral 

 artery ; but it is from the middle cerebral artery alone that the 

 area immediately posterior to and on the same level with the supra- 

 marginal convolution, and this convolution itself, are supplied. 

 When we consider the length and the direction relatively to the 

 carotid of the fissure of Sylvius, the extent of the area to be supplied 

 within it, and the tortuosities necessarily described by an artery pass- 

 ino- along- it to emerge on to the convex surface of the brain, in 

 the words of Duret, /. <?., the ^ pll tres accns^ dans le sillon profond 

 qui separe le lobule de Vinsula de la c'lr convolution inarg'inale ; it is 

 obvious to us that the current of the blood in the terminal arterial 

 twigs supplying the part of the brain in question must be con- 

 siderably slower than that in any portion of the brain situated 

 anteriorly to it. This would be the case even with a system of 

 tubes which were neither contractile nor elastic; that these properties 

 of the arteries supplying this part of the brain may count for much 

 is sometimes rendered strikingly plain to us by their embedding 

 themselves in the substances of the cerebral cortex of brains pre- 

 served in chloride of zinc and alcohol. Several authors ^ have 

 remarked upon the great variability of the cerebral convolutions in 

 the area of which we are treating; there are several reasons how- 

 ever for hesitation as to referring this variability of the topogra- 

 phical disposition of the vesicular neurine to the less vigorous 

 character of the circulation of the blood in the arteries supplying 

 it: but if this peculiarity does not explain the greater morpho- 



^ BiscLofP, Die Grosshim Windmigen des Menschen, Abhandl. Isayer. Akad. der Wiss., 

 cl. ii. bd. X. abth. ii. p. 432, S. A. 42; Ecker, The Convolutions of the HumanBrain, English 

 translation by J. C. Galton, yt. 33. In supj^ort of the view that great differences in 

 functional activity may depend upon hydraulic differences such as those described in 

 the text I may i-efer to the now usually accepted explanation of the phenomenon of 

 right-handedness, to wit, the advantage which the left side of the brain obtains in the 

 matter of irrigation by virtue of the origin of its carotid du-ectly from the arch of the 

 aorta. I take this opportunity of observing that the right cerebral hemisphere is very 

 frequently put at a second disadvantage by the fact that the basilar artery gives it 

 scarcely any supply at all, but distributes itself almost whoUy to the left, lea^•ing the 

 carotid to give off the posterior cerebral artery of the opposite side. This arrangement 

 I had noted pre\iously to becoming acquainted with M. Buret's mention of it (Archiv. 

 de Phys , 1874, p. 68). He does not connect it however with the hydraulic explanation 

 of right-handedness. 



