366 Journal of Comparative Neurology. 



the cortical regions. It contains no Baillarger layer, and only 

 traces of a zonal layer. ^ 



Kaes nowhere gives a' detailed statement of the stage of 

 development reached by each of the regions at different ages, 

 but a general outline of the facts can be gathered from his vari- 

 ous papers. The occipital and central regions are the first to 

 attain any completeness in their medullated fiber systems. In 

 the child of i ]^ years, both regions have reached the point at 

 which the Gennari and Baillarger layers are well marked, and 

 the II and III Meynert layer shows its first medullated fibers.' 

 By 1 8 years all the primary fiber systems of both regions are 

 filled out.* The further course of development consists in the 

 addition of new fibers to the primary system, principally in the 

 II and III Meynert layer,^ and the development of the second- 

 ary fiber system. By about forty years, the central region 

 reaches its highest stage of development, in which the second- 

 ary fiber system is continuous throughout the cortex.* 



The occipital region exhibits its highest stage of develop- 

 ment somewhat later. The second Gennari layer and the sys- 

 tem of secondary fibers are first apparent in the fifty three year 

 brain, and even at that age, the secondary system is not com- 

 plete.*' The posterior frontal region is also well developed in 

 the I ^ year child. The other regions are all in a very rudi- 

 mentary state at this period. None of them have reached the 

 point at which the Baillarger layer appears. Most of them 

 continue to develop slowly throughout life, finally reaching the 

 point described as the limit for each. The anterior frontal re- 

 gion, however, is at a standstill from childhood to about forty- 

 two years, when the Baillarger layers appear. From this time 

 on to fifty-three it years shows a marked development.^ 



^ 6, pp. 12-14. 



* 4, p. 3 ; 6, p. 14. 



* 5. p. 37, p. 47- 



* 3. PP- 38-45- 

 ' 6. p. 5. 



« 6, p. 14. 

 ' 6, p. 13. 



