Thompson, Medullation of Cortical Fibets. 365 



continues to indicate greater development much later than this 

 period.' In spite of this difficulty in interpretation, Kaes is 

 able to deduce from his measurements the general statement 

 that in the adult brain the occipital region is the most highly- 

 developed of any, the central region is a close second, the tem- 

 poral is third, although wide variations are found in it in differ- 

 ent individuals ; the parietal region is fourth and the frontal 

 region is fifth. - 



The determination of degree of development by the 

 complexity of the fiber systems gives almost the same re- 

 sult. Both the occipital and the central regions reach the most 

 complete form, in which the Baillarger and Gennari layers are 

 doubled, and the system of secondary fibers appears.^ The 

 fact that the doubled Baillarger and the secondary fiber system 

 are more marked in the central region would indicate that it is 

 somewhat farther advanced than the occipital region,^ while the 

 measurements placed the occipital region first. The temporal 

 region, which came third in the measurements, shows such wide 

 variations of fiber systems in individuals of the same age that 

 it is difficult to place it. The posterior frontal region is only a 

 little behind the central regions. In it both Baillarger layers 

 are medullated and the system of secondary fibers has begun 

 to appear. The parietal region is somewhat behind the poste- 

 rior frontal. The Baillarger layers are less well marked and 

 there are but a few traces of the secondary fibers. The anterior 

 frontal region, although it develops very late, finally reacjies 

 about the same stage as the parietal. The Island remains in a 

 very rudimentary condition throughout life. It never gets be- 

 yond the point at which the zonal and Baillarger layers first 

 appear. Its II and III Meynert layer never becomes medul- 

 lated. The gyrus fornicatus is the least developed of any of 



16, p. 4; II, p. I. 

 *6, p. 6; 5, p. 35- 

 ' 4, p. 2. 

 *6, p. 13-14. 



