40 Journal of Coiniparative Neurology. 



V. — The dorsal region of the thalamus. 



1. Respecting the epiphysis and dorsal sac there is nothing 

 additional to mention. A comparison of Figures 7 and 9, of 

 Plate VII, with the transverse section, Fig. 5, Plate VIII, shows 

 that the connection of the epiphysis with the third ventricle is 

 direct and that the dorsal sac is greatly restricted basally. 



2. The habena is obviously double and contains small fusi- 

 form cells which give off processes which pass into the taenia 

 cephalad and into Meynert's bundle ventro caudad. The rela- 

 tions are precisely as in Amphibia and if the suggestion of Pro- 

 fessor Fritsch be correct, that the habena of fishes does not give 

 rise to 'nerve fibres and that Meynert's bundle is not nervous, 

 then the like applies to the same structures in Amphibia and 

 Reptilia. Of the homology of the organs with those of higher 

 vertebrates bearing the same names, there can not exist the 

 slightest doubt. The microscopic structure of the habena is 

 shown in Fig. 7, Plate VIII. The nidulus lying below it, in the 

 path of Meynert's bundle, seems to give rise to some of the 

 fibres of the latter and has been called in reptilia Meynert's nid- 

 ulus. The cells are small and resemble those of the habena, 

 Fig. 6, Plate VIII. The longitudinal sections of young speci- 

 mens of Belone, Figs, i, 2, Plate VIII, are designed to show 

 the relation of these niduli to the central gray. 



3. Meynert's bundle maybe readily followed from its origin 

 in the habena almost in a direct line to the interpeduncular nid- 

 ulus, which is double and contains few cells. On the way a 

 number of meduUated fibres are incidentally associated with it, 

 but are not a part of the bundle proper. 



4. In the region adjacent to the habena and dorso-laterad 

 of the dorsal commissure, a vast number of important tracts. and 

 organs are crowded into the narrow space left between the optic 

 tracts. The superior commissure,, in which there is a faint indi- 

 cation of the development of a double system (superior and 

 habena commissures) as described by the writer in reptiles and 

 subsequently, we believe, by Edinger, is well-separated from 

 the posterior commissure and optic tracts. In this space is a 

 multiple nidulus of cells of varying size, which may retain the 

 unfortunate name given it by Fritsch, n. corticalis. From the 

 lateral portion with its large cells, arises the commissura horizon- 



