280 MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 



crus, whilst the occipital passes directly backward. The arrangement is, there- 

 fore, that of a symmetrical, tri-radiate, hollow, nervous bud, separated anteriorly by 

 a depressed fossa, the fossa of Sylvius. 



The Island of Reil, or central lobe of recent writers, develops at the bcttom of 

 this depressed area, directly opposite the point of entrance of the cerebral peduncle 

 and immediately laterad of the corpus striatum, with which it has close and im- 

 portant connections. It is not in any sense morphologically similar to the other 

 lobes of the hemisphere and should not, therefore, be considered in the same light 

 with them. I would, therefore, propose for it the name central nucleus of the cere- 

 bral cortex or lobulus centralis. 



This is evidently the fundamental morphological type or plan of the cerebral 

 hemisphere and I shall attempt to show that the fissures and convolutions of the 

 cerebral cortex are related in a regular and symmetrical manner to these hollow 

 tri-radiate hemispherical buds. 



CEREBRAL FISSURES. 



Before the appearance of the permanent fissures of the hemisphere we find de- 

 veloping towards the end of the third month certain fissures which, with a few ex- 

 ceptions, finally disappear in the fourth month without leaving any trace behind. 

 Tiedemann mentions these furrows and the times at which th.ey appear, but he fell 

 into the error of regarding them as the foundations of the fundamental fissures. 

 Schmidt describes them as appearing in the middle of the third month on the upper 

 surface of the hemisphere as several deep and transverse folds which disappear at 

 the close of the fourth month, stating that they form rather high walls of the lateral 

 ventricles and that the cerebral wall is thinner at these points of folding. 1 Kolliker 2 

 expresses the same opinion and finds that these furrows reach in the fourth month 

 their greatest development; and, with the exception of a few well marked features 

 in the fifth month, again disappear; so that in the sixth month the brain surface is 

 again entirely smooth. My own observations would lead me to agree with Schmidt 

 as I have found that the brain is entirely smooth a little after the close of the 

 fourth month. 



Ecker 3 has also noticed these temporaiw or transient fissures and convolutions. 

 BischofP maintains that these furrows are only artificial productions and arise 

 through plications due to the action of alcohol. He says the hemispheres are 

 smooth up to the moment of the origin of the true or permanent fissures and that 

 in brains hardened in chloride of zinc they do not appear. This is certainly not 

 correct, for I have found them in perfectly fresh foetal brains during the fourth 

 month and Plate XXXV, figs. 1, 2, 3 and 4 show them distinctly in brains that were 

 hardened in chloride of zinc. Ecker expresses the same opinion and also explicitly 



1 Zeitscrhift fur wissenschaftliche Zoologie, Bd. XI, 54. 



2 Entwickelungsgeschichte. 



3 Zur Entwickelungsgescliichte der Furcheu und Windungen auf den Grosshirnhemisphjeren des 

 Menschen und der Affen. Archiv fur Anthropologic, 3er Band. 



* Die Grosshirwindungen 



