THE BRA IX AXD ITS MEMBRANES. 



737 



layer. From their under surface a slender axis-cylinder process arises, which 

 passes through the internal layer, and becomes continuous with the axis-cylinder 

 of a medullated nerve-fibre in the medullary (white) substance beneath. From 

 the other extremity a number of protoplasmic processes (dendrites) are given off, 

 which branch in an antler-like manner in the external layer, all having free 

 terminations. 



The internal or rust-colored layer (Fig. 436) is characterized by containing 

 multitudes of granular-looking cells. There are also minute stellate cells and 

 glia-cells. Between the cells is a fine nerve-network, with which the processes 

 of all the cells are continuous, except the axis-cylinder processes of the granule- 

 cells. 



There are still other fibres to be found in the cerebellar cortex. These come 

 directly from the white centre, and penetrate through the entire cortex. Each 

 fibre, thus penetrating, gives off branches in the granular layer, the ramuscles 

 exhibiting peculiar moss-like appendages, hence are called " moss-fibres " (Ramon 

 y Cajal). Other ramifications are also found around Purkinje's corpuscles. 

 Finally, in the external layer these fibres terminate by becoming longitudinal and 



FIG. 437. A corpuscle of Purkinje, 

 with its dichotomously branched pro- 



P 



FIG. 438. Vertical section of the cerebellum. 



horizontal. The cell-origin of these fibres is probably situated in the gray matter 

 of the spinal cord. 



(2) The independent centres of gray matter in the cerebellum are (1) the cor- 

 pus dentatum : (2) the roof nuclei of Stilling. 



The corpus dentatum (Fisrs. 435. 438), or ganglion of the cerebellum* is situated 

 a little to the inner side of the centre of the stem of white matter. It consists of 

 an open bag or capsule of gray matter, the section of which presents a grav den- 

 tated outline, open at its anterior part. It is surrounded by white fibres ; 'white 

 fibres are also contained in its interior, which are derived from the superior 

 peduncles. 



The roof nuclei of Stilling are two small gray masses situated in the anterior 

 part of the white matter of the worm, close to where the valve of Yieussens 

 begins to assist in the formation of the roof of the fourth ventricle. These can 

 only be seen in microscopic preparations. 



The Fourth Ventricle (Fig?. 423, 429). 



The Fourth Ventricle, or ventricle of the cerebellum, is the space between the 

 mesial portions of the dorsal surfaces of the medulla oblongata and pons ventrally 

 and the cerebellum dorsally. It consists of a floor, roof, and lateral boundaries. 



47 



