203 ANATOMY OF THE CENTRAL NEEVOUS SYSTEM. 



the fissura arcuata. Somewhat dorsal to the fissura chorioidea, which in- 

 dicates, in a measure, the edge of the hemisphere, it runs in a curved course 

 on the inner side of the brain around this edge, thus separating the funda- 

 ment of the marginal conTolution, or gyrus cinguli. The gyrus fornicatus 

 is formed later from the frontal portion of the marginal gyrus, the gyrus 



Fig. 1.35. — The convolutions on the base of the brain (schematic). 

 The chiasma turned baclc. 



hippocampi from its caudal portion. It will be remembered, when it is 

 here learned how early the marginal gyrus is differentiated from the wall 

 of the brain, that in amphibians and reptiles this same region of the brain 



Twas described as that part which possesses phylogenetieally the oldest cor- 



1 tical covering. 



