618 THE NERVOUS SYSTEM 



being noticeably deficient. The stripes of Baillarger, thin layers of 

 tangential fibers on the deeper portions of the cortex, are especially 

 distinct. So many granule cells are scattered among those of the pyram- 

 idal type that it becomes scarcely possible to distinguish from one another 

 the second, third, and fourth layers. When these three layers are in- 

 dividually considered, the type presents eight layers; if, however, they 

 are collectively considered as one stratum, the type presents six layers. 

 With this reservation, the following layers may be distinguished: 



1. Molecular or tangential fiber layer. 



2. Outer polymorphous cell layer. 



3. Small pyramidal cell layer. 



4. The layer of granule and large pyramidal cells. 



5. The outer stripe of Baillarger (great pyramidal plexus). 



6. The granule cell layer. 



7. The inner stripe of Baillarger (polymorphous plexus). 



8. Inner polymorphous cell layer. 



The special characteristics of the visual area are the abundance of tan- 

 gential fibers, as evidenced by the prominent stripes of Baillarger, the 

 thick fiber layer in the deeper part of the molecular stratum, the abun- 

 dance of granule cells, the paucity and irregular form of the pyramidal 

 cells, and finally the presence in the inner stripe of Baillarger and in the 

 outer portion of the deep polymorphous cell layer of numerous large 

 isolated multipolar cells, the giant 'solitary cells' of Meynert. The outer 

 stripe of Baillarger is especially prominent in the visual area (area 

 striata) and is here known as the stripe of Gennari. 



In the auditory area temporal lobe the seven layer type is found. 

 The structure in this area is apparently identical with that previously 

 described for the seven layer type in the parietal lobe. 



In the olfactory area hippocampal gyrus the cells of the outer 

 polymorphous layer arrange themselves in groups, and the pyramidal 

 cells become largely transformed into polymorphic and fusiform cells; 

 these lie between the characteristic outer layer and the inner layer of 

 polymorphic cells, giving to the cortex of this region a three layered 

 structure of indistinct outlines. 



FIBER TRACTS. The corticifugal axons of the cells of the several 

 layers are collected below the upper level of the large pyramidal cell 

 layer into vertical columns which pass to the medulla as the bands of 

 radial fibers. In these same columns course also the corticipetal axons. 

 The cortex thus becomes divided vertically into cell rays and fiber 



