26 "Jounial of Comparative Neurology and Psychology. 



proved the opinion, already generally accepted, that this com- 

 missure does not contain opticus fibers. 



Since I am to describe the nervus opticus of Gadus morrhua, 

 I shall describe the commissures also as they are in the cod. It 

 was, of course, impossible to represent on the drawings the total 

 decussation of the nervt optici (typical for all teleosts — Ramon y 

 Cajal) which, in Gadus, takes place about 0.75 cm. in front of 

 the lobi anteriores. As will be noticed from the drawings of 

 the opticus where it runs under the fore-brain, the two optici 

 are different in my subject. The right nervus opticus is 

 smaller and evidently degenerated and somewhat atrophied 

 and did not take so good a Weigert stain as the left one. 

 This enabled me to examine the relations of the opticus more 

 accurately than under normal conditions, thus controlling and 

 confirming in most respects the experimental investigations of 

 Krause. 



As many figures of serial sections greatly facilitate the descrip- 

 tion and comprehension of the subject, I shall make free use of 

 the figures in treating of the praeinfundibular region. In Fig. xi 

 (Plate I) we see the formation of a part of the commissura trans- 

 versa, viz., the most ventral part, probably the part designated 

 by C. L. Herrick as com. ventralis. A little more caudad 

 (Fig. xxxiv, Plate II) the number of these commissural fibers is 

 considerably increased and we see fibers situated higher up 

 directed toward the median line. 



While the lower fibers of the com. transversa do not in any way 

 touch the bundles of opticus fibers, either proximally or caudally, 

 the upper commissural fibers are seen to be applied to the inner 

 side of the opticus next to the fibrae tectales optici, and to keep that 

 place for some distance, which no doubt led the older investigators 

 to consider them as decussating opticus fibers. That this is not 

 the case I, like Krause, could easily determine by the difference 

 in color of the two optic tracts. The decussating fibers all have 

 the same color and never penetrate more deeply between the 

 opticus bundles. In sections of this region taken somewhat 

 farther caudad (Fig. xxxvi) this is seen clearly. Moreover by this 

 means it is easy to be more sure that there is no difference what- 

 ever either in color or in development of the fibers in the commis- 

 sura transversa. This commissure does not contain any direct 

 optic decussation, on which I can confirm the opinion of Mayser, 



