THE CORTEX AND MEDULLARY CENTER OF THE CEREBRAL HEMISPHERE 287 



neuroglia cells. The nerve-cells are of two kinds: (1) horizontal cells of Cajal, 

 and (2) cells of Golgi's Type II. Within this layer ramify the terminal branches 

 of the apical dendrites from the pyramidal cells of the deeper layers. 



2. The layer of small pyramidal cells (lamina granularis externa) contains a 

 large number of small nerve-cells. Most of these are small pyramids with axons 

 running to the white center of the hemisphere. Others belong to the short- 

 axoned group (Golgi's Type II). 



3. The layer of medium-sized and large pyramidal cells (lamina pyramidalis) 

 may be subdivided into two substrata, the more superficial stratum containing 

 chiefly medium-sized pyramids and the deeper one chiefly large pyramids. There 

 are also present cells of Golgi's Type II and cells of Martinotti. According to 

 Cajal (1900-1906) and Campbell (1905), it is within this layer that the outer 

 stripe of Baillarger is located, but Brodmann places this line in the next layer. 



4. The layer of small stellate cells (lamina granularis interna) is characterized 

 by the presence of a large number of small multipolar cells with short axons 

 (Golgi's Type II). Scattered among these are small pyramids. Brodmann 

 places the outer line of Baillarger in this stratum. 



5. The deep layer of large pyramidal cells (lamina ganglionaris) contains the 

 largest cells of the cortex. In the motor region these are known as the giant 

 pyramidal cells of Betz and give origin to the fibers of the corticospinal tract. 

 The apical dendrites of these cells are very long and, like those of the more super- 

 ficial pyramidal cells, reach and ramify within the molecular layer. Smaller 

 cells, both of the pyramidal and short-axoned type, are also present. The 

 horizontal fibers of Baillarger 's internal line are found in this layer in most of 

 the cortical areas. 



6. The layer of polymorphic cells (lamina multiformis) contains irregular 

 fusiform and angular cells, the axons of which enter the subjacent white matter. 



Cortical Areas. The six layers of the cortex are arranged in most regions 

 essentially as shown in Fig. 215. But each of more than forty areas presents its 

 own characteristic variation in the structure, thickness, and arrangement of 

 the cellular layers, in the thickness of the cortex as a whole, in the number of 

 afferent and efferent myelinated fibers, and in the number, distinctness, and posi- 

 tion of the white striae. On the basis of such differences the entire cortex has 

 been subdivided into structurally distinct areas. Maps of such cortical areas 

 have been furnished by Brodmann (1909), Campbell (1905), and Elliot Smith 

 (1907) ; and while these vary in detail, they agree in their larger outlines. The 

 existence and general boundaries of these regions are now well established; and 



