110 



ANATOMY OF THE CENTRAL NEHTOUS STSTEJI. 



There are also dorsal decussations in the cerebellum. They arise mostly 

 from the Tractus cerebello-spinales, probably also from cerebellar nuclei 

 (see Fig. 210). 



Within the cerebellum there are everywhere associated bundles. The 

 largest of these are found in teleosts, where a large bundle of medullated 

 fibers joins the posterior portion of the cerebellum with the anterior (Fig. 

 86). Then there are always numerous short association-bundles, some of 

 which pass ventral to the Purkinje cells in the inner lamina and a part 

 dorsal to it in the molecular lamina. "What further connections are possible 

 through the medullated nerve-processes may be "better studied in the 

 description of the mammalian brain. 



To Summarize. — In the cerebellum we have an organ into which nerve- 

 tracts enter from the interbrain, the midbrain, the medulla, and the spinal 

 cord: an organ that in mammals is also indirectly connected with the cere- 



Fig. 62. — From the cerebellum of the minnow: Phoxinns lirvis. a, Purkinje 

 cells. 6, Cells of the granular layer, of ^yhich one sends its neuraxons up into 

 the association-net of the zona molecularis (c). 



brum. Into this organ pass bundles from several sensory cranial nerves, 

 especially from the nerves of equilibration. 



Within the cerebellum manifold connections are possible through cell- 

 processes, as well as through contact with the numerous local cells. 



It is easily conceivable that in this range of possible connections with 

 tracts from almost every part of the brain is laid the foundation for co- 

 ordination of movements and for the maintenance of musck-tonus: fimctions 

 which must be ascribed to the cerebellum. 



The loss of the cerebellum has no vital significance in lower vertebrates. 

 It appears that a part of the functions performed by it may be suspended, to 

 be replaced in some way by another part of the brain. Even the minimum 

 development of the organ in creeping animals indicates that it has essen- 

 tially functions which in some way are connected with locomotion. 



