204 The Descent of Man. Part 1. 



" reduit, d'ailleurs flee cctte e'poque. Le reste de la surface cerelDrale 

 * est encore absoluinent lisse." 



Three views of this brain are given in Plate II. figs, 1, 2, 3, of the 

 work cited, shewing the upper, lateral and inferior views of the hemi- 

 spheres, but not the inner view. It is worthy of note that the figure 

 by no means bears out Gratiidet's deserip'i.m, inasmuch as the fissure 

 (anterotempoal) on the posterior half of the face of the hemisphere 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 : 

 a II y a done entre ces cerveaux [ihose of a Callithi ix and of a Gibbon] et 

 " celui du foetus humain une dilfe'rence fondamental. Chez celui-ci, long- 

 " temps avant que les plis temporaux apparaissent, les plis froutaux 

 u essayeiit 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, Bischoff, Pansch, 78 and more particularly by Ecker, 79 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 uterogestation. In this, and in the fourth month, 

 the cerebral hemispheres are smooth and rounded (with the exception 

 of the sylvian depression), and they project backwards 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 Ecker is careful to point out that, not only the time, but 

 the order, of their appearance is subject to considerable individual 

 variation. In no case, however, are either the frontal or the temporal 

 sulci the earliest. 



The fir.-t which appears, in fact, lies on the inner face of the hemi- 

 sphere (whence doubtless Gratiolet, 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 calcarine sulcus, these two beiug close 

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

 occipito-p irietal is the earlier of the two. 



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

 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 

 frontal, 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 (I. c. p. 212-13, Taf. II. figs. 1, 2, 3, 4), the antero- 

 temporal sulcus (scissure parallele) so characteristic of the ape's brain, 

 ts as well, if not better developed than the fissure of Eolando, and is 

 much more marked than the proper frontal sulci. 



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

 of the appearance of the sulci and gyri in the foetal human brain is in 

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



78 ' Ueber die typische Anordnung 79 ' Znr Entwickelungs Geschichte 



der Furchen und Wmduno;ei* auf der Furchen und Wiudungren der 



dea Grosshirn-Hemispbaren des Grosshirn-Hemispharea im Foetus 



Menschen und der Affen.' ' Archiv des Mensc-hen.' ' Archiv fur Anthro* 



(or Anthropologic,' iii., 18G8. pologie,' iii., 1868. 



