TEE CEREBELLUM. 



781 



Fig. 430. 



ventricle • but in the mass of the ortran itself there is no trace of excavation or 

 other peculiarity. This is demonstrated in the most evident manner by sections 

 of its substance made either in an antero-posterior or in a transverse direction. 

 We only see in these, traces of the sulci which divide the organ into lobules ; and 

 they also afford evidence as to the structure of the cerebellum, showing that — 

 like all the other parts of the cerebro-spinal axis — it is formed of ivhite and greij 

 substance. 



The latter — spread over the entire surface of the organ — constitutes the 

 cortical layer of the different segments of which it is composed. It is even 

 prolonged into the convolutions, which increase the surface-extent of the cere- 

 bellum. In each lobule it may be resolved into 

 superposed layers, parallel to the layer of white 

 substance that forms the nucleus of the lobule ; 

 between these layers of grey substance is a very 

 thin mass of white matter. 



The white substancp, enveloped on every 

 side by the grey, forms two thick nuclei 

 occupying the centre of the lateral lobes, and 

 which are united and confounded on the median 

 line in the texture of the middle lobe. 



These two nuclei — in continuity on each 

 side with the cerebellar peduncles — are only 

 their prolongations or intercerebellar portions. 

 They send into the middle of each principal 

 lobule a long and thick branch, which gives off 

 smaller divisions that ramify in the secondary 

 lobules, and from which escape a new series of 

 ramuscules that enter the smallest segments ; 

 this gives to the cerebellum a beautiful arboreal 

 aspect, justly designated by the older anatomists the arbor vita (see Figs. 429, 432, 

 for representations of the arbor vitce cerebeUi). 



In the interior of these nuclei a little in front, there sometimes exists a 

 small, slightly grey streak ; this is the trace of the corpus rhomboideum (or corpus 

 dentatum of Man). 



Stilling has noted two small grey nuclei, which are symmetrical, and are 

 situated in the inferior layers of the middle lobe. 



The nuclei of the white substance of the cerebellum are constituted by nerve- 

 tubes, which are intermixed with numerous nuclei, and are continuous on one 

 side with the crura cerebeUi, and on the other terminate in the cells of the grey 

 substance. 



In the grey streak that forms the corpus rhomboideum, is a great number of 

 large nerve-cells. 



With regard to structure, the grey matter of the cerebellum is made up of 

 three layers ; the superficial is very rich in blood-vessels, has a greyish tint, and 

 is composed of rounded elements, indeterminate in their nature, lying in an 

 amorphous substance ; the middle layer, is composed of Purkinje's cells — large 

 elements disposed in a single row, and provided with ramifying prolongations 

 which are at first directed to the preceding layer, and are then i-eflected downwards 

 into the deep layer, where they are perhaps continuous with the axis-cylinder of 

 the nerve-tubes of the white substance. The latter — also named the rust-coloured 

 52 



ARRANGEMENT OF THE LAYERS AND 

 CELLS OF THE CENTRAL GREY MAT- 

 TER OF THE CEREBELLUM. 



A, White matter. 1, Granulai- or rust- 

 coloured laypr (substantia fcrruginea) • 

 2, layer of Purkinje's cells ; 3, super- 

 ficial amorphous layer. 



