58 "Journal of Comparative Neurology and Psychology. 



Now, taking up the commissura posterior, I have already men- 

 tioned that its anterior -fibers originate from the stratum profundum 

 tecti and end partly in the homonymous stratum of the opposite 

 side, as has already been described by Mayser, and partly lead 

 to the gray substance of the eminentia medialis. To this first 

 part of the commissura posterior I must add those fibers which 

 connect the eminentiae mediales with the tori longitudinales and 

 which certainly are in direct or indirect connection with those 

 fibers of the stratum profundum tecti which enter the torus 

 longitudinalis from its superior side {cf. Fig. xlv with Fig. xlvi). 



The second part of the commissura posterior is formed by 

 fibers which connect with one another the nuclei lentiformes 

 mesencephali, or the medial subventricular cell layers of both 

 sides. This is by far the larger part. The fibers belonging to 

 it form the pars media of the commissure, the more caudal bundles 

 of which (third part) bend downward and backward and run 

 along the aqueduct above the tr. thalamo-spinalis into the most 

 anterior part of that cell-mass from whose posterior part the 

 fasciculus longitudinalis dorsalis arises. 



That fibers of the fasciculus longitudinalis dorsalis continue into 

 the commissura posterior, as C. L, Herrick and Edinger think, 

 is an opinion which I can contradict on the basis of exact investi- 

 gations on Lophius, Gadus, Thynnus, Salmo and Cottus. The 

 results of my investigations agree with those of Auerbach and 

 Van Gehuchten, who state that in the anterior part of the same 

 cell-group from which the fasc. long. post, originate the commis- 

 sure fibers end. I do not consider that thalamus fibers belong to 

 this fasciculus, as Edinger and Johnston do. It arises with 

 heavily medullated fibers in a group of cells of the mid-brain which 

 is the frontal extension of the oculomotorius nucleus, situated 

 immediately behind the most posterior nucleus of the commissura 

 posterior, as Van Gehuchten also mentions. After having 

 arisen (probably with total decussation) in this group of cells, the 

 fibers go backward laterally of the median line immediately under 

 the ventricle and are augmented to a considerable extent by fibers 

 from the oculomotorius and trochlears roots and nuclei. 



As already mentioned in the account of the 'tween-brain, the 

 fibers which Edinger judged to belong of the fasc. long. post, are 

 evidently fibers which have been described by myself and others 

 as thalamo-spinal bundle. These fibers go backward and are 



