126 Journal of Comparative Neurology. 



mesencephalon. Both the above He in the ectal regions and 

 seem to constitute Osborn's direct diencephalic tract. 3. Mey- 

 nert's bundle. 4. Tractus ganglii habenulae ad mesencephalon, 

 fibres passing directly caudad. 5. Tractus descendens ganglii 

 habenulae, with no determinate end caudad. Edinger does not 

 recognize Osborn's commissura infundibularis. From the mes- 

 encephalon, besides the optic tracts, no fibre tracts are recog- 

 nized beside those of the commissura transversa. There re- 

 mains only the pfoccssiis cerebelli ad dieticephalon which is said to 

 arise in the caudal region of the gray matter of the diencepha- 

 lon and pass caudo-dorsad to decussate ventrad of the fourth 

 nerve decussation. 



The following observations may be hazarded : First, as to 

 the basal prosencephalic tract, we do not find all the fibres con- 

 tinuous into the medulla but in Anura sundry connections are 

 formed with the cerebellum via the niger cells. There is also a 

 fine-fibred tract from the thalamic niduli to the mesal or meso- 

 ventral part of the cerebrum. Some of its fibres seem to de- 

 cussate beneath the precommissure, while others pass directly 

 the caudo-dorsal parts of the hemispheres. This mass we homol- 

 ogize with the dorsal or sensory peduncles. 



The tracti thalami, which Edinger derives from the frontal 

 and caudal (or, on the plates, anterior and posterior) niduli of 

 the thalamus we regard as part of the dorsal peduncle system 

 which is continued cephalad as indicated. 



The tractus ganglii habenulae ad mesencephalon we fail to 

 recognize as fully distinct from the optic brachia which follow 

 the course indicated, though arising laterad of the habenae in the 

 geniculata and passing to the inner fibre layer of the tectum. 

 It is important to determine whether the present suggestion can 

 be erroneous ; it is against it certainly that so thorough a mor- 

 phologist as Dr. Edinger could find no cephalic tract from the 

 tectum, although the frog is well supplied with eyes. Yet the 

 brachia exist in fishes and reptiles. (See note at end.) 



The course of the supra-commissure tract in the toad is 

 clearly shown by the transverse section figured. (Plate XVI, 

 Fig. i). The tract passes cephalo-ventrad and laterad from the 



