302 



NORMAL HISTOLOGY. 



Small pyramidal 

 cells 



journey to the surface, the apical dendrite gives off an uncertain number of 

 branches that continue horizontally and, with the collaterals and similarly 

 directed processes from other cells, take part in producing the feltwork giv- 

 ing rise to a thin light band, known as the outer stripe of Baillarger. From 

 the deeper or basal surface of the cell arises the delicate centrally directed 

 a.rone, which, penetrating the intervening fourth layer, acquires a medullary 

 coat and enters the white core of the convolution as one of the component 

 nerve-fibres. The axone gives off one or more collaterals which, after a 

 shorter or longer course, establish relations with clher and often remote cells. 



In addition to the two chief proc- 

 esses, the peripherally directed 

 apical dendrite and the centrally 

 coursing axones, a variable 

 number from four to twelve 

 of secondary lateral dendrites 

 spring from the basal angles of 

 the cell. These processes usually 

 divide dichotomously, each suc- 

 ceeding pair of branches in turn 

 splitting into twigs, until the 

 dendrite is resolved into an end- 

 brush of fibrillae which aid in 

 producing an intricate feltwork 

 of finest threads. Each pyram- 

 idal cell contains a conspicu- 

 ous spherical or ellipsoidal nu- 

 cleus, within which a distinct 

 nucleolus is usually distinguish- 

 able. The cytoplasm exhibits 

 a striation and, in addition to 

 the masses of tigroid substance, 

 the Nissl bodies, a mass of 

 brownish pigment granules. 

 The larger pyramidal cells are 

 surrounded by an evident peri- 

 cellular lymph-space. 



The layer of polymor- 

 phic cells includes a large 

 number of small nerve-cells, 

 from 8-10 fj. in diameter, whose 

 forms vary greatly, irregular, 

 spherical, triangular, stellate 



and fusiform elements being present. Small pyramidal cells are also often 

 seen within this layer. In contrast to dendrites of the typical pyramidal cells, 

 those of the polymorphic elements, although peripherally directed, do not 

 reach the stratum zonale but end before gaining the outermost layer. Their 

 axones pass into the subjacent fibre-layer. The radial disposition of the 

 groups of fibres within the deepest stratum of the cortical substance, limits 

 the polymorphic cells chiefly to the interfascJcular areas, within which the 

 cells consequently appear arranged in a somewhat columnar order. 



Within the deeper layers of the cortex, therefore among the polymor- 

 phic and the pyramidal elements, two additional varieties of nerve-cells are 

 encountered. These are the cells of Martinotti and the cells of Golgi. 



Large pyramidal 

 cells 



FIG. 349. Nerve-ceils of cerebral cortex, after silver im- 

 pregnation. X 70. (Preparation by Prof. T. G. Lee.) 



