I/O Journal of Comparative Neurology. 



collaterals were observed to be given off in the limited distance 

 that they were followed. 



Of the various theories propounded lo explain the function 

 of these interesting structures, that of Fritsch is, perhaps, most 

 plausible, viz., that they have to do with the co-ordination of 

 the action of the lateral musculature in producing the rhythmic 

 movements of the body and tail in swimming, coming into rela- 

 tion with the motor cells of the nerves by means of collaterals. 



In connection with the theory of Fritsch, the discovery by 

 Koppen of large fibers in the caudal myel of certain reptiles is 

 certainly interesting and suggestive. 



There would seem to be no necessary correlation between 

 these fibers and an aquatic life as is thought by some, since 

 they have been found in Aviblysioma, which seems to lead a 

 terrestrial life except during the breeding season. 



The Mauthner fibers correspond closely in their relations 

 with the median crossed Miillerian fibers of the Lamprey,^ 

 which arise (Ahlborn) from large cells near the exit of the 

 auditory nerve, decussate, turning caudad in the myel, where 

 they give off collaterals (Davis) and gradually diminish in size. 



Ventral Tracts. — At the beginning of the metatela, the pos- 

 terior longitudinal fasciculus occupies the same position as in the 

 myel, situated on each side of the raphe, in almost immediate 

 contact with the cells of the endyma, separated only by an oc- 

 casional nerve cell ; in this position it traverses the length of 

 the oblongata, the course being clearly marked in the floor of 

 the ventricle as a white line at each side of the meson. 



In Necturus, an oblique decussation of scattered fibers oc- 

 curs cephalad up to the exit of the caudal root of the tenth 

 nerve ; none was observed between this and the ninth. At the 

 level of the ninth nerve, the root bundle of the seventh has 

 taken its position between this bundle and the endyma of the 



'The statement of Osborn ('88) and Burckhardt ('91) of the occurrence of 

 Mauthner fibers in Petro7iiyzon is inexplicable. The idea may possibly have 

 been gathered from the paper of Fulliquet on the brain of Protopterus , where the 

 Miillerian fibers of the Lamprey, lateral uncrossed, median uncrossed and me- 

 dian crossed, are all called Mauthner fibers. 



