CEREBELLUM OF URODELE AMPHIBIA 9 



tions often appear coarsely varicose and thus distinguishable from 

 others with which they are mingled. Many of them pass at once 

 to the lateral surface of the tegmentum, reaching the surface at 

 about the point of exit of the III nerve. Here they turn caudad 

 and dorsad mingled with terminals of the superficial thalamoped- 

 uncular tract. Having reached the caudal border of the tec- 

 tum, they terminate with widely branched varicose arborizations 

 among the dendrites of the cerebellar neurones (fig. 19, tr.m.ch.). 

 This tract is nowhere condensed into a compact fascicle, but 

 seems rather a special portion of a diffuse hypothalamo-tegmental 

 connection. 



The cerebellar commissure crosses immediately caudad of the 

 recessus posterior mesencephali and its fibers are joined near the 

 medial plane by tracts of veiy coarse medullated fibers from the 

 tectum which enter it from the dorsal and lateral borders of the 

 recessus posterior. These fibers probably include the tractus 

 tecto-cerebellaris and also a part of the mesencephalic V root. 



The decussatio veli consists of separate fascicles of unmedul- 

 lated and fine and coarse medullated fibers. The unmedullated 

 fibers cross the mid-plane farther caudad than the others {comxb.L, 

 figs. 5, 6, 17, 18, 21, 22, 23, 25, 26, 27) and laterally pass into the 

 stratum moleculare of the walls of the lateral recess. Their 

 cellular connections are unknown. In the medial plane the medul- 

 lated fibers of the decussatio veli form a compact fascicle with the 

 coarser fibers farther rostrad. The coarse fibered portion is com- 

 posed partly of fibers of the mesencephalic V root (with which 

 fibers of the IV nerve are mingled), whose relations are considered 

 more in detail below, and partly of fibers of the tractus spino- 

 cerebellaris ventralis. The finer medullated fibers lie adjacent to 

 the unmedullated component and laterally spread out chiefly 

 in the stratum griseum of the body of the cerebellum. The fine 

 fibered medullated component is derived from the cerebellar grey 

 which borders the recessus lateralis on all sides, particularly medi- 

 ally and ventrally. These fibers swing downward and slightly 

 forward from their crossing in the cerebellar commissure to enter 

 the body of the cerebellum, where some of them end. At the 

 junction of this structure with the midbrain the remainder of these 



