274 O. LARSELL 



pear to be, they enter the cerebellum through the region which 

 becomes in higher forms the superior peduncle. 



Fibers are present everywhere in this layer, from one side to 

 the other of the cerebellum. In the more medial region many 

 run anteroposteriorly (fig. 5) rather than transversely, as is the 

 case more laterally in the organ. Close to the median line most 

 of the longitudinal fibers, as seen in sagittal sections, disappear, 

 and the majority of fibers present are cut transversely. These 

 belong for the most part to the cerebellar commissure, but some 

 are fibers of the tractus spinocerebellaris ventralis. 



The granule cells are entirely absent in the median plane (fig. 

 6), but appear as a few scattered cells very close on either side 

 of this plane. The granular layer therefore increases in thick- 

 ness laterally, from a very thin zone containing only a few fibers 

 in the median plane, to a layer which occupies nearly half of the 

 thickness of the lateral portion of the cerebellum. In the last- 

 named region it consists, in addition to numerous fibers, of from 

 twelve to fifteen layers of cells. The few cells present near the 

 median line are located in the posterodorsal portion (fig. 5) of 

 the cerebellum. As the corpus cerebelli is approached, the gran- 

 ule cells not only increase in number, as above noted, but also 

 extend toward the more ventral portion of the cerebellum, until 

 this becomes the thickest portion of the granular layer. This 

 cell layer is continuous with the gray matter of the medulla 

 oblongata. 



In each lateral half of the cerebellum there is present an en- 

 largement of this gray matter which, from its position and from 

 the origin within it of fibers of the brachium conjunctivum, ap- 

 pears to represent the primitive nucleus dentatus (fig. 16, nuc. 

 dent.) already noted in the description of the external form of 

 the cerebellum. 



The fiber tract systems of the cerebellum of Amblystoma corre- 

 spond in general with those of Necturus, but with some modi- 

 fications. The efferent fibers consist of internal arcuate fibers 

 which pass forward and downward into the medulla oblongata 

 and into the midbrain. These are chiefly unmyelinated. They 

 evidently represent the cerebellotegmental system. Only in the 



