THE CEREBELLUM 



891 



medullary laminae surmounted by the foliated cortex, and presenting the charac- 

 teristic appearance known as the arbor vitae cerebelli. 



Isolated Gray Masses or Nuclei of the Cerebellum. Embedded in the white 

 matter of the cerebellum are several gray masses. They are four in number 

 on each side: 



1. Dentate nucleus or dentatum. 



2. Nucleus emboliformis or embolus. 



3. Nucleus globosus or globulus. 



4. Nucleus fastigii or fastigatum. 



The nucleus dentatus is the largest and best studied of the cerebellar nuclei. It 

 is located in the mesal part of the corresponding cerebellar hemisphere, in the direct 

 prolongation of the superior peduncle of the cerebellum, which appears to enter it. 

 It consists of a folded lamina of gray substance convoluted like the similar nucleus 

 of the olive, and opens cephalomesad where its hilum (kilns nuclei dentati] permits 

 of the entrance and exit of fibres from various sources. 



Fig. 656. The peduncles of the cerebellum. On the left the three peduncles have been cut at their 

 entrance into the cerebellum; on the right side they are shown penetrating the cerebellar hemisphere. 

 (Poirier and Charpy.) 



The nucleus emboliformis is a small mass of gray substance, elongated cephalo- 

 caudad, and placed entad of the dentate nucleus, partly covering its hilum. 



The nucleus globosus consists of several small round or oval masses connected 

 with each other and lying entad of the preceding. 



The nucleus fastigii (nucleus of the "roof") is second in size to the dentate 

 nucleus, situated close to the mesal plane directly dorsad of the fourth ventricle, 

 or in the fastigium of the cerebellum, and within the inferior vermis. The nuclei 

 of opposite sides approach each other so nearly as almost to fuse. 



The Cerebellar Peduncles. Three pairs of peduncles constitute the chief avenues 

 for the entrance and emergence of the fibres composing the white substance of 

 the cerebellum and connecting adjacent parts of the brain stem therewith. The 

 peduncles are, on each side, the superior, middle, and inferior peduncles. 



