THE CORTEX AND MEDULLARY CENTER OF THE CEREBRAL HEMISPHERE 285 



midal, (2) the stellate, and (3) the polymorphous cells, as well as (4) the hori- 

 zontal cells of Cajal, and (5) the cells of Martinotti. 



The pyramidal cells are the most numerous and are classified as small, 

 medium, large, and giant pyramidal cells (Fig. 215). From the base of a pyra- 

 midal cell body an axon extends toward the subjacent white matter, giving 

 off collaterals which ramify in the adjacent cortex (Figs. 23, 214, C). The den- 

 drites are of two kinds: a large apical dendrite and numerous smaller ones at- 

 tached to the base and sides of the pyramid. The apical dendrite appears as an 

 extension of the cell body and is directed toward the surface of the cortex, near 

 which it ends in spreading branches. Its length varies with the depth of the 

 cell body from the surface. To an even greater extent than other dendrites it is 

 provided with short thorny processes called "spines" or "gemmules." These 

 are supposed by some to effect contact with neighboring axonic ramifications 

 and to be retractile. Upon retraction of these gemmules, conduction across 

 the synapse would be interrupted for the time being; and one might explain 

 the varying sensory thresholds of an individual in sleep or during attention by 

 the varying degree of expansion of the gemmules. But as yet no satisfactory 

 evidence in support of the theory has been presented. 



The stellate cells are also known as granules. They are, for the most part, 

 of small size, and their short axons branch repeatedly and terminate in the 

 neighborhood of the cell of origin. That is to say, they are cells of Golgi's 

 Type II. Although they occur in most layers of the cortex, they are especially 

 numerous in the fourth stratum, which is accordingly designated as the layer 

 of small stellate cells (Figs. 214, ; 215). 



The cells of Martinotti, which are also found in most of the cortical strata, 

 have this as their distinguishing characteristic, that their axons are directed 

 toward the surface of the cortex and ramify in the superficial layer (Fig. 214, D}. 



The horizontal cells of Cajal, which are present only in the superficial layer, 

 are fusiform, with long branching dendrites directed horizontally. Their axons 

 are long and form tangential myelinated fibers in the superficial layer (Fig. 214,5). 



Polymorphous cells, fusiform or angular in shape, are found in the deepest 

 stratum of the cortex (Figs. 214, 215). Their axons enter the subjacent white 



matter. 



CELL AND FIBER LAMINATION 



The size and type of cells found in the cortex vary at different depths from 

 the surface, that is to say, the cells are disposed in fairly definite layers. As 

 already indicated, many of the myelinated fibers are arranged in bands parallel 



