CEREBELLUM OF URODELE AMPHIBIA 7 



medullary sheaths and other unmedullated connections may 

 occur. 



The ascending spino-cerebellar system is well developed in 

 urodeles, being larger in Amblystoma than in Necturus. There 

 are two of these tracts, a dorsal and a ventral, which in Necturus 

 enter the cerebellum medially and ventrally of the area acustico- 

 lateralis, with which they do not come into relation. 



The tractus spino-cerebellaris ventralis is the larger of these 

 tracts. It ascends in company with the fibers of the tractus spino- 

 tectalis system in the great fasciculus lateralis of the spinal cord 

 and oblongata. In the upper levels of the oblongata this mixed 

 bundle becomes imperfectly separable from the other fibers of 

 the fasciculus lateralis, lying laterally of the large fasciculus bulbo- 

 tectahs, or bulbar lemniscus (Im., figs. 4 to 11 and 27). 



At the level of the superficial origin of the V nerve the mixed 

 bundle (fig. 11, tr.spxb.v.-\-tr.sp.t.) occupies the space between 

 the lemniscus and the motor root of the V nen'e, both components 

 of the bundle being meduUated and at this level indistinguishably 

 mingled. Thej^ continue fonvard along the lateral border of the 

 bulbar lemniscus (figs. 7 to 10) to the level where the body of the 

 cerebellum joins the eminentia ventralis cerebelli in front of the 

 recessus lateralis (figs. 6, 27) ; here the mixed tract turns lateral- 

 ward and divides into its two components. 



The cerebellar component again divides, some of its fibers 

 spreading throughout the adjacent cerebellar tissue, others as- 

 cending as a compact bundle to form most of the coarse fibered 

 component of the commissura cerebelli. The tectal component of 

 the mixed tract turns medialward (fig. 5) and joins the tractus 

 thalamo-bulbaris (figs. 4, 5, tr.th.b.) The further course of these 

 tracts through the mesencephalon I have not followed in Nec- 

 turus; they probably distribute in the same way as in Ambly- 

 stoma, as described below. 



In the upper levels of the oblongata there is a distinct fascicle 

 of medullated fibers immediately ventral to the spinal V tract, 

 whose course cannot be followed so clearly as the tract last de- 

 scribed. Its fibers appear to cross those of the V roots at their 

 superficial origin (fig. 10, tr.sp.cb.d.) and to enter the cerebellum 



