68 



'wor'k, showing the luicleiis in questioi:, luedinl of "(r. olf. tect. sem."). 

 The cells of this nucleus are small. 



Krom this nucleus i)roceeds a new tibr'e tract, running in*a curve 

 in the torus semicircularis, parallel to anil inward of the tr. isthino- 

 teclalis niihi (see below), vet it seems to end in the torus itself. 

 That besides this, fibres should come from the said tract in the path 

 of the tr. tecto-bulbaris or tr. lecto-istlimicus into the tectum, as 

 Hoi,M(5KEN seems (o presume, is improbable to me'). 



As to the origin and the end of nij coarse olfactory fibres, I 

 am (piite unable jet to say an^ything definite. That frontally tliej 

 are connected with the biilbus olfactorius is undoubtedly sure, but 

 their caudal destination remains (piile uncertain. Hoi.mgukn seems 

 to hold the opinion llial his tr. olfactorius lat. optici runs ceiitrifugally 

 ill the o[)ticus (I.e., |). 188). I my.self am more inclined to believe 

 that the fibres of the neutral grouji tend through the path of the 

 commissura transversa towards (he tccluin or, less probable, towards 

 the nucl. [iraerolundus of the other side, the spot where they penetrate 

 into the 0|)ticus root Just coi'responding with the most frontal level 

 of this commissure. This, however, is a mere supposition. 



It is harder slill to say anything of the ilorsa/ group of iriy fibres. 



Concerning the curious olfacto-o|)(ic Inindle in Callionymus, it can 

 only be said that the jiart of ir. olfactorius iiied., that enters frontally 

 into tlie opticus, iHirresponds fairly certainly with the ventral group 

 of my fibres. But about the other part of the tract, the associating 

 opticus fibres, the peculiar nucleus and the bundle originating from 

 it, I cannot give an opinion, as — till now — I have not seen anylhiiig 

 similar with the other bony fishes. 



Summarizing we find in the brain of the Teleosts a remarliable 

 fibre system, connecting the tr. olfactorius with the tr. opticus, 

 consisting in the more primitive forms (Osmerus eperlanus) of thin 

 fibres (that can only be expo.sed by the impregnation method) 

 running in the tr. olfactorius lat., whereas in the more highly 

 organised forms it has coarse, medullary fibres as components and 

 is mixed between the fibres of the tr. olfactorius med. At the present 

 I must be content with confirming Hoi.mgrkn's finding, leaving the 

 arising questions to later investigations. 



II. T/ie Tr. tecto-praerotuitdus. 

 I ihiiik I have discovei'ed in the brain of bony fishes a medul- 



') Holmgren, namely in fig. .S7 of liis work, has indicated this newly forming 

 fibre tract as ,tr. olfacto-tectalis et semicircularis", without further referring to it 

 in the text. 



