THE STRUCTURE OF THE CEREBRAL CORTEX 



267 



of each hemisphere. Some of these fibers are very short, passing 

 between adjacent gyri (arcuate fibers, or fibrae proprise, f.p., 

 Fig. 121); others are very long fibers, forming compact fascicles 

 which can easily be dissected out and which connect the impor- 

 tant association centers of the cortex. All parts of the cerebral 

 cortex are directly or indirectly connected with all other parts 

 by these association fibers, so that no region can be regarded as 

 the exclusive seat of any particular cortical function. 



str term 

 Us. 



f. Tr. OOt 



f.l.i. 

 f. occ.fr. inf. 



Fig. 121. Diagram illustrating some of the chief association tracts of 

 the cerebral hemisphere, seen as projected upon the median surface of the 

 right hemisphere: cin., cingulum; f.l.i., fasciculus longitudinalis inferior; 

 f.l.s., fasciculus longitudinalis superior; /. occ.fr. inf., fasciculus occipito- 

 frontalis inferior; f.p., arcuate fibers; f.tr.oc., fasciculus transversus occipi- 

 talis;/.imc., fasciculus uncinatus; str. term., stria terminalis. 



The human cortex varies in thickness in different regions from 

 about 4 mm. in the motor area to less than half that thickness in 

 some other parts. When cut across and examined in the fresh 

 condition it shows alternate bands of light and dark gray, whose 

 arrangement varies in different parts of the hemisphere. The 

 light bands are composed of myelinated fibers which run parallel 

 with the surface. There are typically two of these light bands, 

 the outer and inner stripes of Baillarger (Fig. 122). In the 

 visual projection area (Figs. 130, 131, area 17) the outer stripe 



