No. I .] DESMOGNA THUS FUSCA . 2 7 1 



of the striatum. Toward the cephalic end of the diencephal 

 there is a good-sized dorsal branch passing up dorso-caudad 

 toward the tectum (Fig. 11). 



The posterior longitudinal fasciculus (hintere Langsbiindel) 

 begins as a well marked bundle in the region of the corpus 

 interpedunculare, and passes through the oblongata into the 

 myel. It is composed of myelinic fibers, and through the 

 oblongata there are many decussational fibers in close relation 

 to these fasciculi, which suggest a comparison to the pyramid 

 tracts of higher forms. In the Desmognathus there is no sharp 

 line of demarcation between the peduncular tracts and the 

 posterior fasciculi further than a less compact arrangement of 

 the fibers at the point where the two systems would be sup- 

 posed to meet. 



In the myel the ventral and lateral columns are not very 

 clearly differentiated from each other. Koppen finds that in 

 the frog the ventral possess larger fibers than do the lateral 

 columns. In the larva of DesmognatJius the fibers of the dorsal 

 columns are easily differentiated from the lateral in Golgi prep- 

 arations on account of their greater coarseness. In the adult 

 this distinction is not so apparent by ordinary methods. The 

 ventral commissure lies just ventral to the myelocoele ; the 

 dorsal commissure is represented by a few transverse fibers 

 which cut off dorsally some of the cells from the central mass. 

 Koppen says that the dorsal commissure is not present in the 

 frog ; but that there are fibers going from side to side, only 

 not joined into a distinct commissure. The Desmognathus 

 shows occasional fibers of large caliber scattered through the 

 ventral columns, as has been noted by Koppen in the frog. 

 These are exclusive of the Mauthner's fibers, which are very 

 distinct in the larva of DesmognatJius and have also been noted 

 in mature specimens, but less constantly. They are situated 

 in the ventral columns, one on each side, at a little distance 

 from the ventral fissure. Time has not permitted the un- 

 raveling of numerous other interesting and complex fiber 

 arrangements in this important region. 



Osborn (38) states that Mauthner's fibers are wanting in 

 most of the Urodela, but records that Stieda had observed them 



