xx Journal of Comparative Neurology. 



opment of the medullary sheaths was used as a check on the results 

 obtained by degeneration. 



Three distinct portions of the optic tracts are distinguished : 

 i. The axial bundle is the first to become medullated and lies ad- 

 jacent to the lumen of the nerve. The fibres cross after entering the 

 diencephalon. This is the bundle which Koppen called the thalamus 

 root of the optic nerve. It may be followed to the roof of the 

 tectum and there dips below the external layer and is lost in deeper 

 cell series. These fibres may be recognized as the most dorsal of 

 those crossing in the chiasm. Wlassak finds, like Bellonci and Her- 

 rick, that the fibres do not terminate in the corpus geniculatum. The 

 fibres end in two layers and form the 3d and 4th fibre layer of the 

 tectum counting from the periphery. 



An attempt to explain the origin of the myelin seems to the 

 writer to rest on very imperfect data. 



2. The second tract is called the marginal bundle and passes super- 

 ficially to the tectum without forming connections in the diencephalon 

 but enters the tectum superficially to the axial bundle. 



Wlassak seems to confuse the Sylvian commissure, which he cor- 

 rectly describes as connecting the two tecta, with the post-commissure. 

 In fact the continental writers generally, since Stieda, have failed to 

 recognize the fundamental difference, though Edinger refers to it. 



3. The third tract is the basal bundle which terminates in niduli, 

 near the median line, cephalad of the oculo-motor niduli, i. e., in the 

 basal optic niduli. 



This bundle is identified with that recognized by Edinger in Am- 

 phibia, and by Singer and Miinzer and Perlia, in birds. Of the in- 

 teroptic commissures one arises in the corpus posterius of Bellonci 

 (testis) and passes mesad of the ventral part of the optic tracts to a 

 decussation with the latter ; the part is identified with inferior com- 

 missure of Gudden. The second part is homologized with Meynert's 

 or Forel's commissure and lies adjacent to the axial optic tract. It 

 finally becomes the most superficial layer of the tectum and termin- 

 ates at the other extremity in the gray matter of the diencephalon. 

 The system receives a new name, " opticoid bundle." 



To the above it may be said that it is wholly incomprehensible, 

 providing no connection between optic tectum and cerebrum. It is 

 also quite inconsistent with results of the present writer. Much 

 would be gained if in the midst of the furor for modern fibre meth- 

 ods and silver impregnation occasional resort could be had to methods 

 which reveal both and stain uniformly. The axis cylinders of the 



