UPON THE SERIES OF PREHISTORIC CRANIA. 271 



zone of the hemisphere. In following- up the distribution of the 

 two terminal branches of the carotid we are impressed with the 

 differentially favourable condition as regards vascular irrigation of 

 the lower parts of the frontal lobes which 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- 

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

 the words of Duret, 1. c, the ' pli tres accuse dans le sillon profond 

 qui separe le lobule de l'insula de la circonvolution marginale ;' 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 1 have 

 remarked upon the great variability of the cerebral convolutions in 



1 Bischoff, ' Die Grosshirnwindungen des Menschen,' Abhandl. bayer.Akad.der Wiss., 

 cl. ii. bd. x. abth. ii. p. 432, S. A. 42 ; Ecker, ' The Convolutions of the Human Brain,' 

 English translation by J. C. Galton, p. 33. In support of the view that great differences 

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

 in the text I may refer 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 directly 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 wholly to the left, leaving the 

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

 I had noted previously 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. 



