66 



pass file fihrae ansulalae of Bpu.oncc, caudo-ventrally descending by 

 and by willi the accompanying tractiis olf.-hypothai. nied. 



Tliese fibres form fhe dorsal gr<)U|) of tbe coarse olfactory fibres. 



Tiie pars 'uitennedia of the tr. oifact. ined. consists half of (he 

 lliinner, and half of the coarser fibres. The first foi'in a small 

 bundle and cross in the commissura anterior (the so-called comm. 

 iiiterbiilbaris). 



The pars ventralis is formed b^' coarse fibres exclusively. They at 

 fii-st Join to a bundle, but fi,radually they separate into several small 

 bundles. These, together with the fibres from the pars iiitei'media 

 form the ventral group of the coai'se olfactory filires. The biiiHlles 

 soon arrange in regular order dorso-ventrally in the pi-aethaiainLis, 

 thereby dorsally touching the tr. olfacto-h3'pothalamicus med., ven- 

 trally the tr. opticus, into wliicii they are taken up gradually (fig. 1). 

 A few tibi-es that are in an exceptional dorsal position, enter into 

 the just rising commissura ndnor. 



Epiphysis 



Telencephalon 



o) the fibres ^* -"^ ' •* 



I'arencephalon 



Tr. ol/'-hypoth. med. with the dors, 

 group of the fibres in question. 



Nuel. 

 praeopt. 



pars 

 magnocell. 



P'ig. 1. Ammodytus tobianus. 

 (Preparation of the Central Institute for Brain-research, Amsterdam). 



With other bony fishes the course of these coarse olfactory fibres 

 is nearly the same. Only the relation to the commissuia minor (and 

 to the fasciculus medialis n. optici) does not always exist, this being 

 most distinct, besides in Ammodytes, with Rhombus, Hippocampus 

 and IMorone. 



1 have been able to find these fibres with Catostomi, Percesoces, 



