72 



steids (few)'), Scorabresocids (part)'), Miigil (the greater part)'), 

 Ophioceplmliis (tiie greater part)'), Morone (greater part)'), Osphro- 

 ineiiiis (part)'), Cottids?'), Cyclopterus?) '), Agoiius?) ') and Trachinus 

 (with the smaller |)art of the fibres)'). 



On the otlier iiaiid tliere are bony fishes in which the bnndle in 

 question can be distinctly followed as far as the frontal tectum 

 section, as Clupea, üyprinidae, Syngnathidae, Osphronienns, Plenro- 

 nectidae (Solea excepted) and Callionymns. I therefore will give here 

 a minute description of the course of this fibre tract in some 

 specimens of fishes. 



Just with Pleuronectes, where Franz believed to have his tr. istbmo- 

 opticus fully established, we can clearly prove that the bundle in 

 question actually enters fiontally into the tectum, in the most super- 

 ficial medullary fibre layer of it. The small bundles namely gather 

 on the lateral surface of the midbrain to a roundish bundle that 

 protrudes into the optic ventricle and then takes a wholly sagittal 

 course, (see lig. 6 of Hippoglossoides). At first it runs ventrally to 

 the bundles of tr. tecto-bulbaris and directly dorsal of the ventral 

 point of the tectum jthite. Some way more frontal it takes the shape 

 of a curved medullaiy plate and encircles about half of the nucl. 

 praetectalis from the lateral side. During this course its position 

 corresponds to the bottom of the tectal furrow characteristic of this 

 fish and, situated caudally deep inside, it frontally more and more 

 apinoaches the outer surface; at last, quite frontal on the level of 

 the geniculatum, it comes close under the molecular layer') of the 

 tectum. Till there it never touches the opticus root. Now part of 

 the bundle radiates caudo-laterally of the geniculatum, towards medio- 

 dorsal into the dorsal part of the tectum*), whereas the other part 

 runs further frontad and finally enters latero-ventrally into con- 

 nection with the ventral part*) of the tectum, which extends a little 

 further frontad than the dorsal one. At this radiation of the bundle 

 I could quite clearly distinguish its small bundles from those of the 

 brachium tecti (Kappers) and the optic root, and prove that the most 

 superficial narrow layer of the so-called opticus fibre layer of the 

 tecliim consists of the little bundles of the fibre tract in question 

 and the next much broader layer of medullary fibres (of the opticus 



1) See note 1 p. 71. 



-I See note 2 p. 71 



') This designation has its explanation in the above-mentioned treatise „On the 

 torus longitudinalis etc.". 



*) The frontal part of the tectum plate is divided into two parts by the afore- 

 mentioned funow. 



