STRUCTURE OF THE BRAIN 271 



The first which appears, in fact, lies on the inner face of 

 the hemisphere (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 Eolando," 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 before the other; and it is 

 remarkable that, in the brain at the period described and 

 figured by Ecker (1. c, pp. 212-13, Taf. II. Figs. 1, 2, 3, 4), 

 the antero-temporal sulcus {scissure parallhle), so character- 

 istic of the ape's brain, is 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 view that man has been evolved 

 from some ape-like form; though there can be no doubt that 

 that form was, in many respects, diflierent from any member 

 ofjthe 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, genus, 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 

 period of its life the tadpole has all the characters of a fish, 

 and, if it went no further, would have to be grouped among 

 fishes. But it is equally true that the tadpole is very differ- 

 ent from any known fish. 



In like manner, the brain of a human foetus, at the fifth 

 month, may correctly be said to be not only the brain of an 

 ape, but that of an Arctopithecine or marmoset-like ape; for 

 its hemispheres, with their great posterior lobes, and with 

 no sulci but the Sylvian and the calcarine, present the char- 



