8 C. JUDSON HERRICK 



dorsally of the ventral spino-cerebellar tract last described. It is 

 probably the tractus spino-cerebellaris dorsalis and has been so 

 named in figures 6 to 10, Some of its fibers may enter the fine 

 fibered component of the commissura cerebelli, though here, as in 

 Amblystoma, most of them evidently end uncrossed. This tract 

 is very distinct in Amblystoma, where it can be followed far back- 

 ward through the oblongata. 



From the entire extent of the area acustico-lateralis internal 

 arcuate fibers descend along the boundary between the stratum 

 griseum and the stratum album. Some of these cross in the 

 raphe; others descend on the same side. From the caudal parts 

 of the cerebellum similar internal arcuate fibers pass downward 

 into the tegmentum and formatio reticularis. These are regarded 

 as the fore-runners of the mammalian tractus cerebello-tegmen- 

 talis system. A part of this system of internal arcuate fibers 

 from both the cerebellum and the anterior lobe of the acustico- 

 lateral area is directed forward into the mesencephalon. These 

 fibers constitute the brachium conjuncti\aim. They arise from 

 the more ventral parts of the cerebellum, none being traced from 

 the dorsal part of the corpus cerebelli. 



The fibers of the brachum conjuncti\iim are chiefly unmedu- 

 lated and pass inward, forward and downward along the lateral 

 border of the stratum griseum toward their decussation in the 

 floor of the midbrain {br.co7ij., figs. 4, 18, 19, 24, 27). The further 

 course of these fibers has not been traced, nor have the cells of the 

 nucleus ruber been identified with certainty. 



In fishes there is a very important connection between the hy- 

 pothalamus and the cerebellum, the tractus lobo-cerebellaris, or 

 better, the tractus mammillo-cerebellaris. A simiar connection 

 appears to be present jn Necturus, though the details have not 

 been fully worked out. The dorsal part of the hypothalamus 

 appears to be the chief efferent center of that region. Fibers of 

 the mammillo-peduncular system arise from its dorsal and lateral 

 surfaces and turn mesad and caudad into the tuberculum poste- 

 rius. Here part of its fibers decussate in the ventral commissure 

 and both direct and crossed portions pass backward into the 

 tegmentum. These fibers are unmedullated and in Golgi prepara- 



