CEREBELLUM 



431 



(Fig. 442). These send only a few short processes inward, but many 

 long processes straight out to the free surface, where they end in triangular 

 expansions. In this way a thick peripheral neuroglia layer is produced. 

 As long as the cerebellar cortex is not fully developed, it presents a 

 series of peculiarities which are lacking in the adult. Thus in embryos 

 and young animals the partly developed gray stratum is covered by a 

 superficial granular layer, the cells of which later become more deeply 

 placed. 



HEMISPHERES. 



The ascending sensory fibers from the thalamus and the parts below, 

 and the descending motor fibers which pass out of the hemispheres are 

 contained in the internal capsule, which is a layer of white substance be- 

 tween the thalamus medially and the basal 

 nuclei of the hemispheres laterally. The path 

 by which these fibers enter and leave the deep 

 white substance of the hemispheres is indi- 

 cated in Fig. 443. Surrounding the inner 

 white substance is the peripheral layer of gray, 

 which forms the cerebral cortex. The cortex 

 is divided into four ill-defined layers an outer 

 molecular or neuroglia layer; a layer of small 

 pyramidal cells; a layer of large pyramidal 

 cells ; and next the white substance, a layer of a .t 

 polymorphous cells. From the pyramidal 



... , .. FIG. 443. TRANSVERSE SECTION OF 



cells the fibers of the descending motor THE BRAIN. About j natural 



size. 



tract arise. The layers are shown in Figs. 444 The gray substance is stippled; the 



white is blank, a. t., Ascending 



and 44 v tract, including the fillet; c. c., 



corpus callosum ; d. t., descendin g 



The molecular layer, which in ordinary sec- tract, leaving the hemisphere to 



enter the cerebral peduncle; n. 1., 



tions appears finely punctate or reticular, con- 



tains besides many neuroglia cells, a network 



of medullated tangential fibers, which are parallel with the surface. Other 

 fibers, as shown by the Golgi method, are partly neuroglia, and partly 

 dendrites of pyramidal cells. The "cells of Retzius" found in this layer 

 have bodies of irregular shape, which send out processes parallel with the 

 surface, and these processes send short branches outward; other processer 

 descend into the deeper layer (Fig. 446). They are probably neuroglia 

 cells. 



The layer of small pyramidal cells contains a special form of nerve cells, 

 with pyramidal bodies measuring 10-12 P.. Since they taper into a den- 

 dritic process, their length cannot be definitely determined. The chief 

 dendrite, after producing small lateral branches, enters the molecular layer 



