NERVOUS SYSTEM 155 



one by Ecker, " Ueber die Entwicklungsgeschichte der Win- 

 dungen und Furchen der Grosshirnhemispharen im Fotus des 

 Menschen " (" On the evolution of the convolutions and fissures 

 of the hemispheres of the cerebrum in the human embryo ";, in 

 the Archiv fur Anthropologie, iii., 1868. A comparison of the 

 results of their investigations has been drawn up by Huxley, 

 and incorporated by Darwin * in his work, On the Descent of 

 Man. Huxley gives the following definitions : 



(1) In the human foetus the fossa Sylvii develops in the 

 course of the third month. During this period and in the fourth 

 month the hemispheres of the cerebrum are smooth and 

 rounded in form and project far over the cerebellum. 



(2) The true fissures first make their appearance between 

 the end of the fourth month and the beginning of the sixth. 

 This, according to Ecker, varies individually. In no case are 

 the frontal or temporal fissures the earliest to appear. The 

 first fissure is either the occipito-parietal or the Hippocampus 

 major. 



(3) Towards the end of this period the fissure of Rolandi 

 is developed, whereupon follow in the course of the sixth month 

 the chief fissures of the frontal, parietal, temporal and occipital 

 lobes. 



Hence Huxley concludes that man is descended from an 

 ape-like type and moreover from one which differed in many 

 respects from all members of the existing order of Primates. 

 The brain of the human embryo in the fifth month may be 

 said to be not merely the brain of an ape but the brain of an 

 Arcopithecus, or of a member of the Marmoset species, though 

 it differs from that of all existing Marmosets by virtue of its 

 open fissure of Sylvius. With respect to the true Platyrrhines, 

 Pausch records that in the brain of an embryonic Cebus Apella 

 only one very shallow fissure was found in addition to the 

 fissure of Sylvius and the Hippocampus. Of great interest in 

 studying the origin of the human brain, is the fact that before 

 temporal, or frontal, sutures appear, the foetal brain of man 

 presents characters otherwise only found in the lowest groups 

 of the Primates (apart from the Lemuridae), and this is precisely 

 what we are led to expect on the theory that man has been 



1 Darwin, loc. cit., v., p. 266. 



