STRUCTURE OF THE BRAIN. 201 



the internal perpendicular (occipito-parietal), or the calcarine sul- 

 cus, 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, how- 

 ever, no clear evidence that one of these constantly appears be- 

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

 period described and figured by Ecker (1. c. p. 212-13, Taf. II. figs, 1, 

 2, 3, 4), the antero-temporal sulcus (scissure parallele) so charac- 

 teristic of the ape's brain, is as well, if not better developed than 

 the fissure of Rolando, 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 evolu- 

 tion, 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, genus, 

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

 mental 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 a tadpole is very different from any 

 known fish. 



In like manner, the brain of a human fcetus, 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 lobster, and with no sulci but the syl- 

 vian and the calcarine, present the characteristics found only in 

 the group of the Arctopithecine Primates. But it is equally true, 

 as Gratiolet remarks, that, in its widely open sylvian fissure, it 

 differs from the brain of any actual marmoset. No doubt it would 

 be much more similar to the brain of an advanced foetus of a 

 marmoset. But we know nothing whatever of the development of 

 the brain in the marmosets. In the Platyrhini proper, the only 

 observation with which I am acquainted is due to 5ansch, who 

 found in the brain of a festal Cebus Apella, in addition to the 



