270 FISH. [Vol. X. 



their relation. According to Koppen (22) they end in the gray 

 substance dorsad of the pars pednncularis. Osborn (38) finds 

 a relationship between the oculo-motor nidus or nucleus and 

 the "pale ganglion cells behind this nucleus." 



The fibers of the optic chiasma sink into the base of the 

 brain, a part of them crossing each other, and at a certain 

 height associating themselves, as has been remarked by Kop- 

 pen, into what is called Haller's transverse commissure. The 

 other, the cephalic bundle of fibers, passes latero-caudad along 

 the thalami and gemina expanding as they go and become 

 associated with the tectum. Osborn (38) finds a tract of optic 

 fibers coming from the prosencephal in both the Urodela and 

 Anura, but states that it requires confirmation. 



The cerebellum is composed largely of myelinic fibers 

 arranged in two bundles of which the cephalic one lies also 

 more dorsal and sends its fibers latero-cephalad into the 

 gemina. They are perhaps comparable to a rudimentary val- 

 vula, Figs. 5, 15, 16. The caudal bundle extends toward the 

 lateral portions of the oblongata and, as has been observed by 

 Osborn and Koppen in other AmpJiibia, bear an intimate rela- 

 tion to the auditory and trigeminus nerves. 



The fibers of a well-marked bundle lying in the diencephal 

 and prosencephal are of both the myelinic and amyelinic variety 

 in the DcsmognatJms. Various names have been applied to 

 this tract. Herrick, in some forms that he has studied, has 

 found it divided and names the parts the dorsal and ventral 

 peduncles. Edinger calls it the basale Vorderhirnbiindel ; 

 Osborn, the basal prosencephalic tract ; Koppen, the rundes 

 Biindel ; Schulgin, the Bahn P. Analogon der Pyramiden. 

 This tract becomes a distinct bundle of fibers in the region of 

 the mesencephal and is situated nearer the ventral portion 

 of the brain. The fibers remain quite compact through the 

 thalami but radiate considerably in the prosencephal. Some 

 of them, as has already been noted, bend mesad to help form 

 the basal portion of the precommissure. Others turn toward 

 the latero-caudal end of the hemicerebrums, while the most of 

 them continue toward the olfactory lobes, but expand in the 

 thickened part of the lateral cerebral walls, — the homologue 



