76 



in the iiucl. praeteclaiis, the brachiuin lecli, who.se lihies are as 

 coarise as the otiiei-s, leaves this iiiicieiis, it is (jiiiie possible that a 

 misinterpretation can arise. All the same 1 can niainlain this point 

 as being quite certain, at least with Exocoetus. When this is the 

 case, these fibres correspond with those of ('atois tVoni the nucl. 

 praetecfalis, of which he writes: "Les antres (fibres)') descendent 

 presque vei-|icalement de la partie inférieure dn noyau pretectal, se 

 recourbent ensuite en arrière et se dirij^ent vers la region basale 

 du mésencéphale" (o|). cit., p. 97). But when he supposes "qn'elles 

 doivent wervir a établir des comiexions entre Ie thalamus et la im^elle 

 spinale" (I.e., p. 97 — 98), thi.s remains a mere supposition, for 

 according lo my investigations we can say for certain that they are 

 connected with iu the ganglion isthnii and conse(piently form a /;•. 

 islhmo-praetecta/is, ") (or i>raetecto-iathmiciis). 



IV. Pars praetectalis Cornm. }ioslerions. 



The component pai'l of the so-called "strnluin zywa/e" of the torus 

 semicircularis, (for convenience' sake I here use this long abandoned 

 nomenclature) is not at all exhausted with the above Ir. istlimo- 

 tectalis mihi and the commissura transversa. With most bony fishes 

 there is namely a fibre connection between tliis stratum and tiie 

 commissura posterior. One bundle from about the middle of tiiis 

 commissure runs latero-ventrally and at the .same lime fronlad, 

 joins the tr. islhmo-lectalis in the most caudal level of the nucl. 

 praetecfalis (tig. 6) or, if this is missing, directly the commissura 

 transversa and then Joins in the characteristic curved course of the 

 torus semicircularis. To the first category, where there is a tr. istlimo- 

 tectalis, belong the Gasterosteids, Belone, Mugil, Ophiocephalus, 

 Moroue, Osphromenus, Pleuronectids, Gobi us, Cottus, Cyclopterus, 

 Agonus, Trachinus and Callionymus, lo the latter, where the tr. 

 istlimo-teclalis is not present, belong .Syndtranchidae?, Esox, Ammo- 

 dytes, Gadids, >Solea, Lophins and Telrodontidae. The fibres of the 

 latter bundle are thinner than those of the tr. isthmo-tectalis. On 

 the other hand thei-e are fishes that have no such connection, e.g. 

 Megalopsr, Clupea.Cyprinoids, Syngnathidae, Exocoetus and Zoarces?. 



This bundle differs from the other components of the commissura 

 posterior by its finer fibres and mostly also by its compactness. As 

 to its position it is about in the middle of the commissure, iu sagittal 



1) Bracketed by myself. 



2) Cf. also Holmqben's drawings of Callionymus: fig. 87, 88 and 89: Tr. ist.- 

 praet. 



