69 



larv fibre tract, not yet described as far as I kiio\v, which probably 

 connects the tectum with ihc nucleus praerotuudus. This tract appears 

 in transverse sections on the ie\ el where tiie fasciculus uiedialis 

 ner\i optici, swinging aci'oss the Ir. >trio-thahuuicus, joins the lateral 

 opticus root. It there appears as a bundle, running dorso-ventrally, 

 medially along the dorsal opticus root. Dorsaliy it lies in separate 

 bundles between the just-mentioned opticus root and those fibres 

 that branch off «more fronlally) from the tr. opticus, run dt)rsad in 

 the post-habenular region and finally lateral into the deep medullary 

 layer ledum. From these fibres probably corresponding to the 

 fibrae tectales n. optici of Kh.msk) the tract is distinguished by 

 the smaller caliber of its fibres and its steeper course. Somewhat 

 more caudally it bends in a lateral direction and eiHers also into 

 the deep medullary layer of the tectum. 



V^entrally it crosses with the fasciculus med. n. o[)tici directly 

 medially to the praetectal nucleus, then runs laterally down from 

 the tr. strio-thalaraicus, to finally join the fibres of the commissura 

 transversa (see fig. 2). 



Often, however, it does not run laterally to the Ir. strio-thidamicus 

 but medially, together with the fasciculus med. ii. optici towards 

 medioventral, consequently in this case delusive of a commissura 

 minor in the sense of Ahiëns K.^ppurs (one-sided in a specimen of 





Tr. 

 tecto- *** 

 praerot. ~^ 

 mihi 



Br. tccti 

 post. 



Tr. strio-thal. 



Comm. HEURICK 



Tr. tccto-praerot. mihi 

 Fasc. med. n. opt. 

 (Comm. Herrick failing here) 



Fig. 2, Mugil chelo. 

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



