BRAIN OF MAN AND THE BRAINS OF CERTAIN ANIMALS. 39 



where phrases it), we are always justified, if we can recognise the 

 suture which limits the frontal from the parietal bone, in saying" 

 that under it will be found lying the convolution numbered 4 *. 

 I know not what, nor whether any, functions have been localised 

 along this sutural arc. Our third and last great boundary line is 

 the so-called external perpendicular fissure which is lettered E in 

 the Diagrams. It is upon the upgrowth in man within this fissure 

 of convolutions (lettered a and (3 in the Diagrams), stunted else- 

 where, that so much weight has been laid. They are in him 

 connecting table-lands elevated from the lower position of spurs 

 and sloping declivities. (See Figures 3 a, 3 b.) We see them 

 neither in the chimpanzee nor in the mandrills. (See Figures 4 b, 

 5 a.) The external perpendicular fissure (IE) has taken their place. 

 In the orang (Fig. 4 a) and the Ateles (Fig. 5 b) we again see the 

 letters a and /3 which betoken them. The lobe numbered 10, 11, 

 12, which they connect with one numbered 5 and 4, is the occipital ; 

 the one numbered 5 and 4 is the parietal. The fissure of Sylvius 

 separates this lobe from the temporo-sphenoid, numbered 7, 8, 9. 

 The lobe in front of the parietal numbered 1, 2, 3 is the frontal. 

 We have become acquainted then with four great divisions in the 

 brain surface, and that each admits of an easy division into three 

 minor convolutions the diagrams sufficiently show. I shall not 

 enumerate all the twelve with their distinctive peculiarities and 

 several grades of development ; the three divisions — the upper, 

 lower, and middle stages as they may be called — of the frontal 

 lobe are, however, of importance to us even in this hurried and 

 imperfect comparison. The bridging convolutions have in name 

 the physiological importance of a primary lobe ; morphologically, of 

 course, they cannot hold this rank. A lobe hidden from our eyes, 

 and in the depths of the Sylvian fissure, holds just the reverse 

 relation to morphological and physiological considerations, it is 

 present in all the subjects of our comparison, and is the centre 

 point round which the other convolutions can be most naturally 

 grouped; but physiologically it is of little moment; known as 'the 

 island of Reil ' it completes the number, five, of which we spoke as 

 being the number of the great brain divisions. 



1 [Gratiolet was in error in placing this convolution under the fronto-parietal suture, 

 for the fissure of Rolando is always situated some distance behind that suture. — 

 Editor.] 



