130 NERVOUS SYSTEM. 



Aphasia = loss of power to talk amnesic when words are for- 

 gotten ; ataxic when the power to articulate is -lost, though the 

 words are known. 



THE CEREBELLUM. 

 Describe the cerebellum. 



It is a mass of nerve-substance situated posteriorly at the base 

 of the skull. It consists of a median lobe and two lateral hemi- 

 spheres, and is connected with the rest of the cerebro-spinal system 

 by numerous white fibres collected in bundles known as peduncles. 

 Of these, the larger peduncles pass to and largely make up the pons 

 Varolii (middle peduncles), thus connecting the lateral hemispheres 

 of the cerebellum. The superior peduncles (or processus e cerebello 

 ad testes) pass beneath the corpora quadrigemina, and the fibres pass 

 into the white matter of the cerebrum, decussating as they meet 

 beneath the corpora quadrigemina. The inferior peduncles pass to 

 the medulla, where they form the restiform bodies. Thus it is seen 

 that the entire cerebro-spinal system communicates very freely with 

 the cerebellum. 



How is the gray matter of the cerebellum arranged ? 



The arrangement in convolutions is not the same as in the cere- 

 brum, but there are numerous transverse sulci which divide and 

 subdivide, the gray matter being disposed about them in a thin 

 layer. This causes a section of the organ to have a peculiar tree- 

 like appearance, which originates the name, " arbor vitas,'' given to 

 the cortical matter of the cerebellum. Besides this, there is a cen- 

 tral collection of gray substance the corpus dentatum. 



What peculiarities does the gray matter of the cerebellar cor- 

 tex possess ? 



Under the microscope it is found to consist of three layers (Fig. 37). 

 The outer is a layer of delicate connective tissue which supports 

 fine nerve-fibres and small spindle-shaped, branching nerve-cells. 

 The middle layer is characterized by irregularly disposed large gan- 

 glion-cells, and the branching processes from these ramify in the 

 superficial layer. These cells are known as Pitrkinjes cells. The 

 inner layer is made up of a mass of small spheroidal cells, and 

 gradually merges into the white substance. 



What is the function of the cerebellum ? 



The cerebellum seerns to exert no influence upon the sensory 



