270 THE DESCENT OF MAN 



tlie other of a human foetus at the 22d or 23d week of utero- 

 gestation, in which Gratiolet notes that the insula was un- 

 covered, but that, nevertheless, "des incisures s^ment le 

 lobe ant^rieur; une scissure peu profonde indique la sepa- 

 ration du lobe occipital, tres-r^duit d'ailleurs d^s cette 

 ^poque. Le reste de la surface cdr^brale est encore abso- 

 lument lisse." 



Three views of this brain are given in Plate II., Figs. 

 1, 2, 3 of the work cited, showing the upper, lateral, and 

 inferior views of the hemispheres, but not the inner view. 

 It is worthy of note that the figure" by no means bears out 

 Gratiolet's description, inasmuch as the fissure (antero- 

 temporal) on the posterior half of the face of the hemi- 

 sphere is more marked than any of those vaguely indicated 

 in the anterior half. If the figure is correct, it in no way 

 justifies Gratiolet's conclusion: "11 y a done entre ces cer- 

 veaux [those of a Callithrix and of a Gibbon] et celui du 

 foetus humain une difference fondamentale. Chez celui-ci, 

 longtemps avant que les plis temporaux apparaissent, les plis 

 frontaux essayent d'exister." 



Since Gratiolet's time, however, the development of the 

 gyri and sulci of the brain has been made the subject of 

 renewed investigation by Schmidt, Bischofl:, Pansch," and 

 more particularly by Eoker," whose work is not only the 

 latest, but by far the most complete, memoir on the subject. 



The final results of their inquiries may be summed up as 

 follows: 



1. In the human foetus, the Sylvian fissure is formed in 

 the course of the third month of utero-gestation. In this 

 and in the fourth month the cerebral hemispheres are smooth 

 and rounded (with the exception of the Sylvian depression), 

 and they project backward far beyond the cerebellum. 



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

 interval between the end of the fourth and the beginning of 

 the sixth month of foetal life, but Bcker is careful to point 

 out that not only the time, but the order, of their appear- 

 ance is subject to considerable individual variation. In no 

 case, however, are either the frontal or the temporal sulci 

 the earliest. 



'8 "TJeber die typisehe Anordnung der Furchen und 'Wiiidungen auf den 

 GrossWm-HemiBpharen des Menschen und derAffen." "Arcliiv fur Anthro- 

 pologie," iii., 1868. 



" "Zur Entwickelunga Geschichte der Furchen und Windungen der 

 GroBshirn-Hemispharen im ffoetus des Menschen." "Archiv fur Anthropolo- 

 gie," iii., 1868. 



