204 The Descent of Man. Part I. 



" re'duit, d'aiileui-s dos cctte e'poque. Le reste de la sui-face ce'rebrale 

 " est encore absolument lisse." 



Three views of this brain are given in Plntp II. figs, 1, 2, 3, of tlie 

 wnrk cited, shewing the upper, lateral and iiiferi"r views of the hemi- 

 spheres, but nut the inner view. It is worthy of note that the figure 

 I }' no means bears out Grratiolet;'s description, inasmuch as the fissure 

 lanterotempo'al) on (he posterior half of the face of the hemisphere ia 

 more marked than any of those vaguely indicated in the anterior half. 

 If the figure is correct it in no way justities Giatiolet's conclusion : 

 " II y a (lone entre ces cerveaux [those of a Callithiix and of a Gibbon] et 

 " nelui du foetus humain une difference fondamental. Chez celui-ci, long- 

 " temps avaut que les plis tcmporaux apparaissent, les plis frontaux 

 *' t'SKuyei't d'exister." 



Since Gratiolets time, howevrr, the development of the gyi-i and 

 su'ci of the brain has been made the subject of reneweil investigation 

 by Solmridt, Bischoff, Pansch,^' and moie particulaily by E ker,™ whose 

 work is not only the latest, but by far the most complete, memoir on 

 tlie subject. 



The final results of their iiiquirirs may be summed up as follows : — • 



1. In the human foetus, the sylvian fissure is formed in the course of 

 the thiid mouth of uterogestation. In this, and in the fourth month, 

 the cerebral hemispheres aie smooth and rounded (with the exception 

 of the sylvian depression), and they project backwards far beyond the 

 ceiebellum. 



2. Tlie sulci, properly so called, begin to appear in the interval 

 between the end of the fourth ami the beginning of the sixth month of 

 foetal life, but Ecker is careful to point out that, not only the time, but 

 the order, of their appearance is subject to considerable individual 

 vaiiation. In no case, however, are either the frontal or the temiioral 

 sulci the eailiest. 



The first which appears, in fact, lies on the inner fa"e of the hemi- 

 sphere (whenre doubtless Gratinlet, who does not seem to have examined 

 that face in his foetus, overlooked it), and is either the internal perpen- 

 dicular (occipito-parietal), or the cah'arine sulcus, these two being close 

 together and eventually running into one another. As a rule the 

 occipito-parietal is the earlier of the two. 



3. At the latter part of this period, another sulcus, the " pnsterio, 

 parietal," or " Fissure of Rolando '' is developed, and it is followed, in 

 the course of the sixth month, by the other principal sulci of the 

 fiontal, parietal, tempoial and occipital lobes. There is, however, no 

 clear evidence that one of these constantly appears before the other; 

 and it is remarkable that, in the brain at the period described and 

 figured by Ecker (1 c. p. 212-13, Taf. It. figs. 1, 2, 3, 4), the antero- 

 terapnral sulcus {scissun paralUle) so characteristic of the ape's brain, 

 IS as well, if not better developed than the fissure of Kolando, and is 

 much more marked than the proper frontal sulci. 



Taking the facts as they now stand, it appears to me that the order 

 jf the appearance of the sulci and gyri in the fcetal human brain is in 

 perfect harmony with the general doctrine of evolution, and with the 



'* ' (Jeber die typische Anordnung '^ ' Z'\r Entwickelungs Geschichte 



Jer Furchen und Windungec auf der Fuichen und Windungen der 



den Grosshirn-Hemispbarea des (irosshirn-Hemispharen im Fcetus 



Menschen und der Affen.' ' Archiv des Mcnschen.' ' Archiv fiir Anthro- 



fi*r Anthropologie,* iii., 18C8, pologie,' iii., IP i8. 



