THE HIND-BRAIN. 



691 



enter the cerebellum beneath the middle peduncle ; passing upward they end in 

 the gray cortex of the upper surface of the hemisphere, some being prolonged into 

 the white matter of the superior vermiform process. The following are the chief 

 sets of fibres in the inferior peduncles : (1) from the direct cerebellar tract of the 

 spinal cord ; (2) from the gracile and cuneate nuclei (crossed and uncrossed fibres) ; 

 (3) from the opposite olivary body of the medulla ; (4) fibres to the nuclei of the 

 fifth, eighth, ninth, and tenth nerves ; (5) descending cerebellar fibres which pass 

 down the restiform body and antero-lateral column of the cord to terminate around 

 the cells in the anterior horn of the cord. 



The fibrae propriae of the cerebellum are of two kinds : (1) commissural fibres, 

 which cross the middle line to connect the opposite halves of the cerebellum, some 

 at the anterior part, and others at the posterior part of the vermiform process ; (2) 

 arcuate or association fibres, which connect adjacent laminae with each other. 



The gray matter of the cerebellum is found in two situations : (1) on the 

 surface, forming the cortex ; (2) as independent masses in the interior. 



1. The gray matter of the cortex presents a characteristic foliated appearance, 

 due to the series of laminae which are given off from the central white matter ; these 

 in their turn give off secondary laminae, which are covered with gray matter. This 



Punctated 



molecular 



layer. 



FIG. 367. Diagrammatic representation of the cells of the cerebellum. (Modified from Foster's " Physiol- 

 ogy.") A, molecular layer ; B, nuclear layer ; C, white matter. 



arrangement gives to the cut surface of the organ a foliated appearance (Fig. 366). 

 Externally, the cortex is covered by pia mater ; internally, is the medullary centre, 

 consisting mainly of nerve-fibres. 



Microscopic Appearance of the Cortex. The cortex presents a remarkable 

 structure, consisting of two distinct layers, viz., an external gray molecular layer, 

 and an internal, rust-colored, granular layer. Between the two layers is an incom- 

 plete stratum of the characteristic cells of the cerebellum, the corpuscles of 

 Purkinje. 



The external gray or molecular layer (Figs. 367, 368) consists of fibres and cells. 

 The nerve-fibres are delicate fibrilla;, and are derived from the following sources : 

 (a) the dendrites and axon collaterals of Purkinje's cells ; (b) fibres from cells in 

 the granular layer ; (c) fibres from the central white substance of the cerebellum ; 

 (d) fibres derived from cells in the molecular layer itself. In addition to these are 

 other fibres, which have a vertical direction. These are the processes of large 

 glia-cells, situated in the granular layer. They pass outward to the periphery of 

 the gray matter, where they expand into little conical enlargements, which form 



