Her RICK, Morphology of Brain of Bony Fishes. 37 



Passing adjacent to the optic tract it accompanies the anterior 

 division to the region near the entrance of the latter into the 

 tectum, where it is interrupted in a cell mass from which springs 

 the cephalic brachium of the tectum. 



3. The commissura minor forms the most dorsal of the sys- 

 tems. Its relations to the other commissures will be obvious on 

 the comparison of Fig. i, Plate VI, with Fig. 6, Plate IV. It 

 is one of the most perfect commissures of the brain and its sharp 

 dorsal curvature after crossing is characteristic. It lies far re- 

 moved from all other tracts and is quite unambiguous. Its fibres 

 pass to the interval between the two branches of the optic tract, 

 perhaps to the same region as the com. transversa. It appears 

 not to have been described unless it was included by Mayser as 

 a dorsal portion of the transversa. 



4. The commissura horizontalis (Fritsch) is the most distinct 

 of these systems and is mentioned m connection with several 

 other organs. Its strong band of large fibres forms a distinct 

 loop across the median line and by a gentle reverse curve passes 

 to the nidulus ruber, passing through it in a curved course, 

 emerges and, with the cephalic peduncle of the cerebellum, enters 

 the nidulus corticals adjacent to the habena. It was adequately 

 described by Mayser, who, however, could not determine its 

 relations to the posterior commissure. Its crossing and a part 

 of its upper course is shown in Fig. 5, Plate IV. In Fig. 6, it 

 occupies the centre of the ruber. Its union with the anterior 

 peduncle is seen in Fig. 2, Plate V. Fig. 2, Plate VI, shows a 

 greater part of its course from the ruber to the corticalis. 



It should be noticed that this commissure is curiously sinu- 

 ous in its course, first turning dorso-caudad, then is depressed 

 by the crossing of the dorsal peduncles so that in Fig. 5, Plate 

 IV, it appears twice. 



5. Immediately ventrad of the horizontal commissure a 

 small but very distinct bundle of very small fibres forms a com- 

 missure {com. superior tuberi), which pursues a curiously tortuous 

 course ; passing caudo-ventrad, then plunging ventrad, lying 

 mesad of the ventral peduncles (Figs. 3, 4, Plate IV); thence 

 it passes caudad of the latter to the lateral aspect of the cephalic 

 cornu of the hypoarium, where it again turns dorsad and caudad 

 and loses an independent existence by mingling with the fibres 



