THE MOTOR AREA 



511 



I 



layer is covered by a marginal veil of neuroglia homologous with 

 that beneath the pia mater of the spinal cord. 



The second, or outer polymorphous cell layer, is a thin stratum. 

 Its cells are frequently clumped, thus forming groups of various 

 size. This grouping is, however, more 

 distinct in some other regions, e. g., the 

 olfactory area, than in the motor area 

 itself. 



The third layer, small pyramidal cells, 

 is somewhat thicker than the above. It 

 consists of numerous small cells tri- 

 angular, pyramidal, or pyrif orm in shape 

 whose pointed apices are directed toward 

 the surface. Three sets of dendrites are 

 given off by these cells, an apical process 

 which passes outward to ramify in the 

 outer molecular layer, and from either side 

 of the base of the cell a second set, whose 

 processes are distributed in a plane nearly 

 corresponding to that in which their cell 

 bodies lie. The neuraxis is usually given 

 off from the basal surface of the cell, and 

 passes from this point directly inward to 

 the white matter of the cerebral medulla. 

 These small pyramidal cells are not very 

 deeply stainable, and according to the 

 classification of Nissl fall under the 

 parapyknomorphic arkyochrome variety. 



The fourth layer, that of the large py- 

 ramidal cells, is also a thick layer. Its cells 

 are of the same shape, and distribute their 

 processes after the same manner as those 

 of the small pyramidal cell layer. Accord- 

 ing to the classification of Nissl, however, 

 these giant pyramids are deeply stainable, 

 or pyknomorphic arkyochrome cells. The 

 motor area is specially characterized by 

 the large size of the cells of this layer. 



The fifth, or inner polymorphous cell layer, is thinner than the 

 preceding. Its cells are of very varied form pyramidal, stellate, 

 fusiform, and granule cells and are less densely packed than is 



' _ J 



FIG. 395. HUMAN CORTEX 



CEREBRI, MOTOR AREA. 



a, tangential fibre layer; 



i, outer polymorphous cells; 



o, small pyramidal cells ; d, 



large pyramidal cells ; *, 



inner polymorphous cells. 



Nissl's stain. Moderately 



magnified. (After Schlapp.) 



