THE CEREBELLUM OF AMBLYSTOMA 281 



passes into the lobus auricularis. Within the auricular lobe 

 fibers pass dorsally and mesad from the main bundle (figs. 17 to 

 21, r.VIII). Most of these disappear among the cells and fibers 

 of the auricular lobe, but many appear to pass into the corpus 

 cerebelli. The VIII tract continues forward, diminished in 

 size, to the most rostrad region of the auricular lobe, where its 

 fibers disappear in a manner similar to those in the more caudad 

 portion of the lobe. 



The lateral-line roots of the VII nerve can be followed as small 

 bundles of myelinated fibers forward into the auricular lobe. 

 Four distinct bundles can be recognized in the adult Ambly- 

 stoma at most of the levels between the superficial roots of the 

 facialis and the auricular lobe. These apparently are the con- 

 tinuation of the four roots of the lateral-line component of the 

 VII nerve described by Coghill ('02). The three more dorsally 

 located (figs. 17 to 20, r.VII U.d., r.VII U.m., and r.VII l.l.m'.) 

 could not be followed with certainty beyond the posterior region 

 of the auricular lobe, but the ventral tract (fig. 21, r.VII l.l.v.) 

 continues dorsal to the VIII tract to terminate in the rostral 

 end of the auricular lobe. 



SUMMARY 



The cerebellum of Amblystoma has the general characteristics 

 of this organ as described in other urodeles, but it shows some 

 advances of structure and organization not present in the lower 

 forms of this group of vertebrates. 



The more important of these advances are : 1) increased size of 

 the corpus cerebelli; 2) the presence in the corpus cerebelli of a 

 group of cells which appear to foreshadow the nucleus dentatus; 

 3) the presence of a definite zone of Purkinje cells, the cells of 

 which have the general characteristics of this type of neurone as 

 present in higher vertebrates; 4) the presence of granule cells 

 and moss fibers within the substantia grisea, which corresponds 

 to the stratum granulare of higher forms. 



The principal fiber-tract connections, with modifications of 

 detail, are similar to those of lower urodeles. These include the 

 tractus spinocerebellaris ventralis, the tractus spinocerebellaris 



