67 



Acanthopterygii and Plectognathi, but not witli Malacoptervgii, Osta- 

 riophysi, Symbranchii and Haplomi. Tlie}' probably are neither to 

 be found with Anacanthini and PediruUxti (at least not medulhited). 



The quantity of the fibres varies according lo the iiind of fislies. 

 It often is so small that the (ibres can be easdy counted. In any 

 case the fibres are generally not very numerous. The ventral group 

 is always superior in number to ihe doi'.ml, which I even cannot 

 find in Solea and Cottus. 



With Callionymus lyra, the very bony fish that Holmgren examined, 

 the matter is somewhat different. 



Inasfar as it may l)e judged by Weigert-Pal series these fishes 

 show IK) tr. olfactorius lat. The tr. olfactorius med. is fairly coarse 

 and is found as usual on the medio-\enlral side of the frontal half 

 of the brain. Caudally it soon descends a little ventrally already 

 before the level of ilie commissura rninoi', and comes in touch with 

 the opticus fibres and especially willi those that arrive here from 

 lateral. I think it faiily probable thai fibres are being exchanged 

 between these two iracts, tliat is to say that tr. olfactorius gi\es 

 away a part of its fibres to the tr. opticus, but in exchange receives 

 more fibres from the latter tract during its descension (see below) 

 and so becomes visibly coarser. The fibre tract now runs medially 

 along the dorsal opticus root in a ventral direction. ') More frontal 

 a small part of the Ir. olfactorius is separated from the chief bundle 

 on the spot where this trad begins to descend in order to come 

 into touch with the w. opticus. This separated little bundle runs 

 independently in the praethalamus also ventrad, about in the middle 

 of the inner and outer surface of .same, and finally joins again the 

 principal bundle. ') 



When the tlni> formed olfacto-oplic liinidle has at last left Ihe 

 tr. opticus, it runs lateral, viz. between the tr. strio-thalamicus med. 

 and the nucl. anterior thalami'r'). More caudally it wedges between 

 the nucl. jiraerolundus? ') and the tr. tubero-dorsalis of Goldstein. 

 A little way back nerve cells begin to appear in tiie bundle and 

 finally take up the area of the bundle nearly entirely. This nucleus 

 takes its place quite superficially of the lateral surface of the hypo- 

 thalamus, close above the lobus inferior (see fig. 87 pf Holmgren's 



'") The formation of the very extensive tectum plate and accordingly the topo- 

 graphy of the opticus roots are in this bony fish difïerent from others. 



') So with Gailionyraus nearly all medullary olfactory fibres seem to run as far 

 as into the praethalamus. 



') I have not yet succeeded in identifying these nuclei free from objection with 

 this fish. 



5* 



