14 C. JUDSON HERRICK 



Study of the mediillated fiber tracts of the brain of Amphiuma 

 ('oufinns the description given above for Necturus in almost every 

 point. Both dorsal and ventral spino-cerebellar tracts are pre- 

 sent. The system of internal arcuate fibers from the cerebellum 

 and area acustico-lateralis (tr. cerebello-tegmentalis) is well devel- 

 veloped, most of these fibers descending to decussate in the same 

 transverse plane as their cells of origin. But few medullated 

 fibers of this system are directed forward to decussate under the 

 mesencephalon. That is, the brachium conjunctivum is either 

 unmedullated or very feebly developed. 



The decussatio veli lies relatively farther ventrally than in 

 Necturus. The unmedullated and fine fibered medullated com- 

 ponents of the cerebellar commissure are similarly related in the 

 two species. The coarse medullated fibers also seem to be simi- 

 larly related to the mesencephalic V root and the tractus spino- 

 cerebellaris, the former fibers greatly predominating. In Nec- 

 turus the relation of these coarse fibers of the commissure to the 

 tectum mesencephali is obscured by their mingling with those of 

 the decussating IV nerve; but in Amphiuma the reduction of the 

 IV nerve to a small vestige comprising less than 10 medullated 

 fibers renders a clearer analysis possible. Here it can be easily 

 seen that by far the greater number of these coarse commissural 

 fibers after their decussation turn forward to enter the tectum for 

 distribution to the large cells of the mesencephalic V nucleus. 

 One small fascicle of such fibers ascends directly dorsally from 

 their decussation near the medial plane to reach the cluster of 

 mesencephalic V cells lying in the roof of the recessus posterior 

 mesencephali. Few, if any, root fibers of the trigeminus in Am- 

 phiuma terminate in the cerebellum; they traverse this structure 

 to reach their cells of origin in the tectum mesencephali. 



