THE CEEEBELLUM. 



107 



brate classes; but sufficient work has not yet been done with developmental 

 or degeneration methods. Accept what is here presented as simply that 

 which may be with some certainty now expressed. 



The cerebellum stands in connection with other parts of the brain 

 through its "peduncles. The fiber constituents of the peduncles are, for the 

 most part, constant, except that in the lower vertebrates appear certain 

 tracts not yet found in mammals and birds, while in mammals there is a 

 cerebral connection which is peculiar to this class. 



Least Imown as to their real origin are several frontal tracts. In 

 teleosts, whose large cerebellum contains easily recognizable afferent tracts, 

 two tracts pass from the thalameneephalon: a fine-fibered posterior one and 



Decuss. valvuia: 





Tr. tegmento-cerobellaria 



/Molecular Layer and cells < 

 1 Parkiiije 



Pars dorsal. Ganglii Isthmi 



/ 



Qrannlar layer 

 Tr. cerebello-spinalis 



— •Nerrus acusticua 



Fig. 60. — Section through the velum and cerebellum of a large 

 lizard: Lacerto muralis. 



a coarse-fibered frontal one, the first into the cerebellum and the second into 

 the Valvuia cerebelli, the portion which lies under the roof of the mid- 

 brain. These are called Tractiis thalamencephalo-cerebellares. These bundles 

 have not, with certainty, l^een found in other animals. The Brachium con- 

 junctivum anterius or superior cerebellar peduncle, is always present as 

 the Tractus tegmento-cerebellaris. This is a bundle from a ganglion, which 

 lies at the posterior end of the base of the thalameneephalon. jSTot far from 

 its origin it decussates with its fellow. This decussation, which always lies 

 at the level of the Oculo-motorius near the base, is a good point of orienta- 

 tion in investigations in brain-anatomy. Thence the fibers pass dorsally 

 into the cerebellum (see Figs. 59, 61, 71, 83, 84, and 85). 



Besides the tract named, still other fairly large bundles enter the 



