6 C. JUDSON HERRICK 



spino-cerebellaris, tractus hypothalamo-cerebellaris, tractus tecto- 

 cerebellaris, and perhaps other tracts. Their neiirites are directed 

 in part forward into the brachium conjunctivum, as illustrated, 

 and partly downward and backward under the recessus lateralis 

 in the tractus cerebello-tegmentalis. Figure 20 shows two smaller 

 neurones from a point farther dorsal in the medial wall of the 

 anterior diverticulum or corpus cerebelli. 



The white matter of the cerebellum consists of a superficial 

 neuropil and of certain well defined fiber tracts which are partly 

 medullated. The neuropil (stratum moleculare) covers the entire 

 external surface and also extends along the medial border of the 

 anterior diverticulum of the recessus lateralis into the region of 

 fusion between the diverticulum and the mesencephalon (figs. 4, 5, 

 23) . The medullated fibers of the cerebellum accumulate chiefly 

 in the area of fusion just referred to, i.e., along the external border 

 of the ventricular grey, as in the higher Amphibia. The general 

 plan of the fibrous connections of the cerebellum is not funda- 

 mentally different from that of the area acustico-lateralis which 

 occupies a similar position in the rhomboidal lip farther caudad. 



The fiber connections of this region, so far as revealed by the 

 Weigert method, have accurately described by Kinsgbury ('95, 

 p. 174), whose description I have confirmed, though a thorough 

 study of the arrangement of the neurones and unmedullated fibers 

 would yield much additional information. Fibers of the VIII 

 nerve and the lateral line roots of the VII and X nerves spread 

 throughout the area acustico-lateralis, but the precise regions of 

 distribution of these several roots have not been determined. 

 Internal arcuate fibers pass into the medial raphe from the entire 

 region, and there are two strong uncrossed medullated association 

 bundles running between its rostral end and the parts of the 

 oblongata farther caudad. One of these runs in the dorsal and 

 one in the ventral part of the acustico-lateral area and they are 

 termed by Kingsbury respectively 'tract a' and 'tract b' (figs. 

 10, 11, 21, 22, 23). Neither these tracts nor any root fibers of the 

 VIII or lateral line nerv^es can be traced forward in Weigert prep- 

 arations from the area acustico-lateralis into the cerebellum, 

 though these fibers may take this course after the loss of their 



