270 GENERAL REMARKS 



either by disease or by accidents. Fourthly, the comparison of 

 the brains of human beings of various known capabilities and 

 ages with each other and with the brains of the lower animals 

 which are nearest to man casts a diffused, if not a concentrated light 

 upon the entire enquiry. Arguments bearing upon this question 

 may be procurable from other sources ; of the four specified the first 

 furnishes us with the least ambiguous and the most readily verifiable 

 indications; with these the indications furnished by the other three, 

 if not connected in the way of effect with cause, are at all events 

 correlated in the way of concomitant growth. 



A survey of the distribution of the several arteries x supplying the 

 cerebrum appears to show unmistakeably that the particular zone of 

 convolutions in question is at unmistakeable disadvantage in the 

 matter of irrigation as compared with the segments of the hemi- 

 sphere which lie in front of it, and that of two brains of equal or 

 approximately equal length that one is the more favourably con- 

 ditioned which has this segment contributing the smaller factor 

 towards making up its total length. 



The belt of convolutions which interposes itself between the line 

 of the lambdoid suture and another line drawn parallel to either half 

 of that suture over the parietal tuberosity of that side receives its 

 main arterial supply from the terminal twigs of that branch of the 

 internal carotid which is known in this country as the * middle 

 cerebral ' artery, but which for the present purpose might bear one 

 of its foreign names, viz. ' arteria fossae SylvhV For it is only after 

 having supplied the very numerous and extensive convolutions 

 which form the floor and the walls and the margins of this great 

 fossa that terminal branches of this artery emerge on to the ex- 

 terior convex surface of the brain and distribute themselves to this 



1 Some difference of opinion exists between the two investigators, MM. Duret and 

 Heubner, who have ('Archives de Physiologie Normale,' 1874, torn, vi., and ■ Central- 

 blatt fur die Med. Wiss.' 1872, 'Die luetische Erkrankung der Hirnarterien,' 1874, pp. 

 172-175) been investigating the cerebral circulation, as to the degree of freedom with 

 which the arteries in question anastomose with each other. Heubner however, who 

 specially insists upon the formation in the pia mater of a common retiform reservoir 

 by all the brain-supplying arteries in a common solidarity, nevertheless allows, as the 

 facts of pathological embolism even more than those of experimental injection compel 

 him, that the different parts of this reticulation are filled from the different main 

 arteries with differing facility ; ' von dem entfernteren natiirlich schwerer und lang- 

 samer als von dem naheren.' This is all that need be asked for justifying the argu- 

 ment in the text. 



