THE CEREBELLUM 323 



THE CEREBELLUM 



The cerebellum consists of a middle lobe, called the 

 vermis, and two lateral lobes. The grey matter upon its 

 surface is divided into two layers, an outer molecular 

 layer composed of interlacing fibres, and an inner granular 

 layer of small nerve-cells. At the junction of these layers 

 are situated the cells of Purkinje, large cells whose axons 

 pierce the subjacent white matter to terminate in the deep 

 nuclei of the cerebellum. The latter are four masses of 

 nerve-cells, the nucleus dentatus, nucleus emholiformis, 

 nucleus globosus and nucleus fastigii. By its three 

 peduncles the cerebellum makes the following connec- 

 tions : — 



Afferent Tracts : — 



1. With the spinal cord, by uncrossed fibres arising in 

 the cells of Clarke's column travelling up {a) in the direct 

 cerebellar tract, inferior peduncle, and terminating in the 

 vermis; (6) in the indirect cerebellar tract, reaching the 

 vermis by the superior peduncle. 



2. With the medulla, and thus indirectly with the spinal 

 cord, by fibres arising (a) in the nucleus gracihs and 

 nucleus cuneatus; (6) in the ohve. These fibres pass up 

 by the inferior peduncle and are chiefly crossed, 



3. With the vestibular nerve. 



4. With the pons, by fibres arising in the nucleus pontis, 

 crossing the mid-line, and terminating in the cerebellar 

 cortex. Through these the cerebellum comes into con- 

 nection with the cerebral cortex of the opposite side. 



5. With the mid-brain, by fibres from the anterior cor- 

 pora quadrigemina. This tract gives connection with the 

 optic nerves. 



Efferent Tracts. — ^These arise in the deep nuclei. 



1. Fibres from the nucleus dentatus passhig by the 

 superior peduncle to the red nucleus and optic thalamus 

 of the opposite side. 



2. A few fibres to the nuclei pontis of the opposite side. 



