THE MESENCEPHALON. 



581 



branches, which enclose the cells of Purkinje, as well as the short non-medullated portions 

 of their axons, in a close basket-work of fine filaments. 



The granular layer is, for the most part, composed of large numbers of small 

 granule -like bodies closely 

 packed together. Each of 

 these possesses a somewhat 

 large nucleus, with a very 

 small amount of surround- 

 ing protoplasm. From the 

 cell body three or four, or 

 perhaps five, dendrites and 

 one axon proceed. The 

 dendrites are short and 

 radiate out from different 

 aspects of the cell body. 

 They end in tufts of claw- 

 like twigs, which either 

 embrace or are otherwise in 

 contact with neighbouring 

 granule cells. The whole 

 multitude of granule cells, 

 therefore, are brought into 

 intimate connexion with 

 each other. The axon 

 passes into the molecular 

 layer, in which it ends, at 

 a varying distance from the 

 surface, by dividing into 

 two branches. These di- 

 verge so sharply from each 

 other that they form almost 

 a right angle with the parent 

 stem, and they run parallel 

 to the long axis of the p. 



FIG. 515. TRANSVERSE SECTION THROUGH A CEREBELLAR FOLIUM 

 (after Kolliker). 



Treated by Golgi's method 



Axon of cell of Purkinje. 

 Moss fibres. 



folium, threading their way 



among; the branches of the K and Kl * Fibres from white core of folium ending in molecular layer in 



connexion with the dendrites of the cells of Purkinje. 



various dendritic planes of M> Small cell of the molecular layer. 



the cells of Purkinje and GR. Granule cell. 



entering into contact associ- GrR 1 . Axons of granule cells in molecular layer cut transversely. 



ation with them. When it M '- Basket-cells 



:- j J.L A At, ZK. Basket-work around the cells of Purkinje. 



i borne in mind that the GL Neuroglial cell> 



number of granule cells N. Axon of an association cell. 



is very great, and that 



each sends an axon into the molecular layer, the important part which these fibres, 



with their longitudinal branches, take in building up the molecular layer will be under- 



stood. They are found pervading its entire thickness from the surface down to the 



bodies of the cells of Purkinje. 







THE MESENCEPHALON. 



e mesencephalon or mid-brain is the short, narrow part of the brain-stem 

 which occupies the aperture of the tentorium cerebelli (incisura tentorii), and 

 connects the cerebrum, which lies above, with the parts which occupy the posterior 

 cranial fossa. It is about three-quarters of an inch in length, and it consists of a 

 dorsal part, composed of the corpora quadrigemina, and a much larger ventral part, 

 which is formed by the two pedunculi cerebri. 



The pedunculi cerebri can be seen to some extent on the base of the brain, 

 where they bound the posterior part of the interpeduncular fossa. Encircling the 

 upper end of each cerebral peduncle, where it emerges from the cerebrum, is the 

 optic tract (Fig. 527, p. 594). 



The mesencephalon is tunnelled from below upwards by a narrow passage, 

 called the aquseductus cerebri, which connects the fourth ventricle with the third 



386 



