23S THE DESCENT OF MAN. 



sulci of the brain has been made the subject of renewed investigation 

 by Schmidt, Bischoff, Pansch,* and more particularly by Ecker,+ 

 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 formeci 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 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 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 first which appears, in fact, lies on the inner face of the hem- 

 isphere (whence doubtless Gratiolet, who does not seem to have 

 examined that face in his foetus, overlooked it), and is either the 

 internal perpendicular (occipito- parietal), or the calcarine 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 " 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, temporal and occipital lobes. There is, however, 

 no clear evidence that one of these constantly appears laefore the 

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

 and figured by Ecker (1. c, p. 212-213, Taf. II, figs. 1, 2, 3, 4), the 

 antero-temporal sulcus {scissure parallele) so characteristic of the ape's 

 brain, is as well if not better developed than the fissure of Rolando, 

 and is much more marked than the proi)er 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 view that man has been evolved from some ape-like 

 form; though there can be no doubt that that form was, in many 

 respects, different from any member of the Primates now living. 



Von Baer taught us, half a century ago, that, in the course of 

 their development, allied animals put on at first, the characters of 

 the greater groups to which they belong, and, by degrees, assume 

 those which restrict them within the limits of their family, genius, 

 and species; and he proved, at the same time, that no developmental 

 stage of a higher animal is precisely similar to the adult condition of 

 any lower animal. It is quite correct to say that a frog passes through 

 the condition of a fish, inasmuch as at one x^eriod of its life the tad- 

 pole has all the characters of a fish, and if it went no further would 



"Ueber die typische Anordiiunj; derFurchen und Windunfren auf den 

 Grossbim-IIeniispharen des Menschen und der Affen." " Archiv. fur Anthro- 

 pologie," iii, 18(58. 



t " Zur EiitwickolunffS fleschichte der Furchen und Wiiuhinge i der Gross- 

 hirn-llemispharen im Foetus des Menschen." " Archiv. fur Antliropologie," 

 iii, 1868. 



