4l6 THE CENTRAL NERVOUS SYSTEM. 



in all parts of this layer, but are more numerous in its peripheral 

 portion. They are multipolar cells with neuraxes which are not 

 readily stained and concerning the fate of which little is known. 



The granular layer contains two varieties of ganglion ele- 

 ments, the so-called granular cells (small ganglion cells) and the 

 large stellate cells. The dendrites of the granular cells are short, 

 few in number (from three to six), branch but slightly, and end in 

 short, claw-like telodendria. Their neuraxes ascend vertically to 

 the surface and reach the molecular layer. At various points some 

 of them are seen to undergo a T-shaped division, the two branches 

 then running parallel to the surface of the cerebellum in a plane 

 vertical to that of the dendrites of the cells of Purkinje. Large 

 numbers of these T-shaped neuraxes produce the striation of the 

 molecular layer of the cerebellum. It is very probable that during 

 their course these parallel fibers come in contact with the dendrites 

 of the cells of Purkinje. The large stellate cells are fewer in 

 number and lie close to the molecular layer, some of them even 

 within this layer. Their dendrites branch in all directions, but 

 extend principally into the molecular layer. Their short neuraxes 

 give off numerous collaterals which end in telodendria among the 

 granular cells. 



The medullary substance is composed of the centrifugal neu- 

 raxes of the cells of Purkinje and of two types of centripetal neu- 

 raxes, the mossy and the climbing fibers. The position of their 

 corresponding nerve-cells is not definitely known. The mossy 

 fibers branch in the granular layer into numerous twigs, and are 

 not uniform in diameter, but are provided at different points with 

 typical nodular swellings. These fibers do not extend beyond the 

 granular layer. The climbing fibers pass horizontally through the 

 granular layer, giving off in their course numbers of collaterals, 

 which extend to the cells of Purkinje, up the dendrites of which 

 they seem to climb. 



In the medullary portion of the cerebellum are found a number 

 of groups of ganglion cells known as central gray nuclei. The 

 nerve-cells of these nuclei are multipolar, with numerous, oft- 

 branching dendrites and a single neuraxis. 



C THE CEREBRAL CORTEX. 



The cell-bodies of the neurones of the cerebrum are grouped in 

 a thin layer of gray matter, varying in thickness from 2 to 4 mm., 

 which, as a continuous sheet, completely covers the white matter 

 of the hemispheres, and in larger and smaller masses of gray mat- 

 ter, known as basal nuclei. In our account of the histologic struc- 

 ture of the cerebral hemispheres we shall confine ourselves in the 

 main to a consideration of the cerebral cortex, the thin layer of 

 gray matter investing the white matter. 



