280 O. LARSELL 



it appears quite evident that some of the fibers of the combined 

 tract terminate within the cerebellum, so that the designation, 

 tractus mammillocerebellaris, is employed. 



The mesencephalic V tract (figs. 19 to 21, mes.V) has not 

 been studied by the writer except in its relation to the cerebel- 

 lum. It is composed of coarse myelinated fibers which form a 

 well-defined bundle of characteristic appearance. This bundle 

 passes dorsorostrally and mesad from its origin at the superficial 

 roots of the trigeminus toward the mesencephalon. In its 

 course it traverses the cerebellum and for a short distance is 

 more or less intermingled with the cerebellar commissure (fig. 

 19). The fibers of the mesencephalic V tract, however, may be 

 distinguished from those of the commissure. They merely pass 

 through the latter in their course between the midbrain and V 

 nerve. In the boundary region between the cerebellum and 

 the tectum, however, the mesencephalic V fibers become inter- 

 mingled with others, especially those of the IV nerve, in such a 

 manner that they are difficult to follow in Weigert preparations. 

 Their further course has not been studied. So far as observed, 

 they have no immediate functional relation to the cerebellum. 

 The trigeminal fibers previously noted which appear to pass into 

 the cerebellum have no relation, so far as could be determined, 

 to the mesencephalic V tract. 



There are some indications of tectocerebellar fibers, but they 

 do not form a distinct tract and are so intermingled with other 

 fibers in this region that a clear analysis was not possible. 



The fiber tracts which pass into the auricular lobe have much 

 the same relationship in adult Amblystoma as they have in the 

 larval form, so far as the available material indicated. 



The VIII tract forms a well-defined bundle of fibers which lies 

 close to the lateral margin of the area acustica. From its origin 

 at the level of the VIII nerve to a point slightly rostrad of the V 

 root, two bundles, a dorsal and a ventral, may be observed in 

 adult Amblystoma. This is the condition observed by Herrick 

 in the larval form, except that the two tracts are distinct only 

 as far as the superficial origin of the V root in the latter. The 

 fibers continue forward from this point as a single tract which 



