204 



ANATOMY OF THE CENTEAL NBHVOUS SYSTEM. 



with from the study of the adult brain. The Sylvian fossa, the origin of 

 which was earlier explained, becomes narrower; the wall of the brain around 

 about it grows and soon hangs down over it on all sides. sThe insula begins 

 to disappear at the bottom of the fissure; the edges of the fossa approach 

 one another more and more, and finally meet toward the end of festal life. 



Fig. 137. — Large scar on the outer side of a cerebrum. All the convolutions con- 

 verge toward the point where the brain could not expand. (After Ziegler.) 



The fissura Sylvii, with its branches, now alone affords access to the fossa 

 over the insula Eeilii, which was at one time wide open. 



By the end of the fifth month the fundament of the central fissure has 

 appeared dorsal to the fissure of Sylvius. 



Gradually, in the course of the sixth and seventh months all the other 



Fig. 138. — Brain at the end of the seventh month. 



fissures follow the few fissures just mentioned. But they are still so little 

 branched and so simply arranged that a glance at a fetal brain at the end 

 of the seventh month is sufficient in order to survey at once the most im- 

 portant parts of the fissuration of the brain (Fig. 138). 



That which here lies before us resembles a schema of the fissures of the' 



