238 



NERVOUS SYSTEM OF VERTEBRATES. 



there is a deep commissure accompanied by nuclei which will be 

 described below. In all vertebrates the cerebellum has two 

 brachia, a posterior and an anterior. The posterior bracliium 

 contains primarily fibers belonging to both somatic and visceral 

 sensory systems. As already described, primary root fibers of the 



Fig. 121. — A diagrammatic transverse section of one fold of the cerebellum. 

 From Koelliker. /, moss fibers; gl, glia cells; gr, granules; gr', neurites of gran- 

 ules seen in the molecular layer; k, net-like fibers; k', endings of the same; m, 

 small cells of the molecular layer; in', basket cell; zk, pericellular basket of the 

 same; n, short neurite of large granule. 



somatic sensory nerves and external arcuate (secondary sensory) 

 fibers enter the cerebellum in all vertebrates. In lower verte- 

 brates the secondary gustatory tract runs ventral to and parallel 

 with the somatic sensory tracts and ends in the secondary gustatory 



