73 



fibre layer), se|iarate(l from tlje first by a strand of grey substance, 

 oonsLsts of the small bundles of llie brachium tecti and the tr.' opticus 

 (see fig. 4j. 



Also with Clupea, examined likewise by Fhanz and drawn by 

 him in fig. 9 of his treatise, I could trace the fibre tract as one or 

 two coarsefil)red bundles above and partly through the lateral opticus 

 root, lateral of the praetectal nucleus and the geniculatum, as far as 

 in the upper fibre layer of the n)0St frontal tectum (fig. 5). 



With the Cyprinidae its course is about the same as with Clupea. 

 Tlie small bundles gather medio-dorsally to the lateral root in one 

 or two bundles, then run frontad, at first between the nuol. prae- 

 tectalis and the lateral opticus root, then between the nucl. anterior 

 thalami and the ganglion geniculatum. Here a part of the fibres 

 branches oïï into the tectum, but the remainder runs, dorsally to the 

 geniculatum, further fi'ontad, then turns medio-dorsad and finally 

 also reaches the tectum. 



By the way I want to remark that with these Teleosts (Pleuro- 

 nectids, Clupea and Cyprinids) the bundle in question is accompanied 

 in its entire frontal course by the tr. geniculo-myelencephalicns of 

 Holmgren. The two bundles, however, can easily be distinguished, 

 the fibres of the first bundle being far coarser than those of the 

 latter. 



With Osphromenus the bundle shows a peculiarity. Part of its 

 fibres enter, as mentioned above, already caudallj' into the lateral 

 opticus root. Here again I expected to be able to trace the small 

 bundles through the complex of the opticus fibres right into the 

 upper fibre layer of the tectum. The other part, however, turns in 

 the subependymal layer gradually medio-dorsad, above the comm. 

 horizonlalis fibre group'), and finally enters into the fibre system 

 of the most medio-frontal tectum part. 



Therefore I am fully convinced that there is no doubt but the 

 bundle in question, that is to say what Franz calls tr. isthnio-oplicus, 

 does not run in the opticus to the eye, as Franz presumes, Itul to 

 the frontal tectum, and there becomes part of the opticus fibre layer. 

 Also in those cases where the fibres concerned enter already caudal 

 into the lateral opticus root, it may be assumed that we have the 

 same state of affairs as I have been al>le to prove in Osphromenus. 

 In the following I shall call the bundle provisionally tr. isthmo- 

 tectalis, although the direction of its course (ascending or descending) 

 is not have proved yet. 



') Complex of commissura horizonlalis and tr. teclo-cerebellaris (cf. fig. 5). 



