82 H. ■ V. NEAL 



Belogolowy ('10a, p. 367-8) describes the histogenesis of the 

 trochlear, which may be summarized as follows : The first devel- 

 opmental stages of the nerve take place in the brain. Here the 

 fibers of the brain are gradually differentiated as processes of 

 cells in the somatic motor column of the hindbrain. The fibers 

 grow in the direction of the dorsal side of the brain and toward 

 the constriction between second and third brain vesicle, that is 

 toward the basis of the cerebellum anlage. The fiber bundles 

 may be easily traced through the brain wall and usually number 

 three. 



At the time when these bundles have reached a point about 

 two-thirds the height of the neural tube a nidulus of large gang- 

 lion cells makes its appearance at the place of the future point of 

 emergence of the fibers. The evidence of their ganglionic char- 

 acter consists in their larger size and in the outgrowth of fibers 

 from them. (Belogolowy 's figures, however, do not bear out 

 the latter assertion.) This dorsal nidulus is gradually enclosed 

 by the spongiosa and penetrated by the coarse fibers of the troch- 

 lear until only isolated cells remain scattered in the region of 

 the chiasma. The bundle of fibers of the nerve anlage is at first 

 free of accompanying cells, which appear first at about the level 

 of the middle of the brain wall. 



Belogolowy then goes on to present evidence that the accom- 

 panying cells can have nothing to do with the genesis of the fibers 

 of the trochlear. Notwithstanding the divergence in his account 

 in regard to the existence of a dorsal nidulus, Belogolowy does 

 not hesitate to compare the trochlear with typical somatic motor 

 nerves. He agrees with the conclusion that connection between 

 hindbrain and superior oblique muscle is secondary, an inference 

 which — in the light of the evidence now in our possession — there 

 seems no good reason to doubt. 



c. Have these protoplasmic connections a genetic relation to the 

 neurofibrilsf As first stated by Kastschenko ('88, p. 465) the 

 trochlearis, from the time of its first appearance, is a fibrillar 

 structure. In preparations of Squalus embryos by the Vom- 

 Rath method these fibers are deeply-staining and highly refract- 

 ive threads, contrasting strongly with the protoplasm of the ad- 



