THE CONNECTIONS OF THE CEREBELLUM 



709 



The peculiar position of the latter toward the cells of Purkinje gives rise to very close 

 and multiform synapses so that the widest possible ramifications are established. 

 Functionally, this intricate union of the different neurons greatly facilitates the 

 spreading and summation of impulses, and leads to the so-called avalanche conduc- 

 tion, i.e., to an unusually extensive involvement of neurons. 



The Connections of the Cerebellum. — The cerebellum is expanded 

 upon a central stem formed by its three connecting strands of fibers, 

 which are known as the superior, middle and inferior peduncles. 



Fig. 355. Fig. 356. 



Fig. 355. — Basket-work of Fibers Around Two Cells of Purkinje. 

 a, Axis-cylinder or nerve-fiber process of one of the corpuscles of Purkinje; h, fibers 

 prolonged over the beginning of the axis-cylinder process; c, branches of the nerve-fiber 

 processes of cells of the molecular layer felted together around the bodies of the cor- 

 puscles of Purkinje. (Cajal.) 



Fig. 356. — Figure Showing the Three Pairs of Cerebellar Peduncles. 



On the left side the three cerebellar peduncles have been cut short; on the right 

 side the hemisphere has been cut obliquely to show its connection with the superior 

 and inferior peduncles. The cut ends of the cerebellar peduncles have been artificially 

 separated from one another and are displayed diagrammatically. 1, Median groove 

 of the fourth ventricle; 2, the same groove at the place where the atlditory striae emerge 

 from it to cross the floor of the ventricle; 3, inferior peduncle or restiform body; 4, 

 funiculus gracilis; 5, superior peduncle: on the right side the dissection shows the 

 superior and inferior peduncles crossing each other as they pass into the white center 

 of the cerebellum; 6, lateral fillet at the side of the pedunculi cerebri; 7, lateral grooves 

 of the pedunculi cerebri; 8, corpora quadrigemina. (From Sappey after Hirschfeld & 

 Leveille.) 



The superior peduncle is made up very largely of fibers which arise in the dentate 

 nuclei.and pass toward the region of the midbrain. They cross the midline below 

 the corpora quadrigemina and connect with the red nucleus and the optic thalamus. 

 The afferent fibers of this peduncle are few in number and seem to be derived from 

 the thalamus. 



The middle peduncle is made up chiefly of afferent fibers which are derived from 

 the nuclei of the pons. They cross the midline within this structure and pass into 

 the lateral cerebellar hemisphere of the opposite side. A certain number of fibers 

 also extend efferently from the cerebellum into the same region of the pons. In this 

 way, a connection is formed with the corticopontine fibers which brings the cere- 



