No. 5.] HABENULAR TRACTS OF ACIPENSER. 233 



The two nuclei of the corpus striatum described above are 

 not sharply differentiated. Since the fibers from the tractus 

 olfactorius are found to end in the internal nucleus and have 

 not been seen to end elsewhere in the striatum, this nucleus is 

 probably homologous with the epistriatum as described by 

 Edinger ('96a, b) in reptiles, amphibia, and teleosts. The cells 

 of the external nucleus give rise to descending fibers of 

 the tractus strio-thalamici, and are therefore to be considered 

 as the motor component of the corpus striatum. In the 

 intermediate portion there is a mingling of cells of the two 

 kinds, and hence a region of mixed functions. It seems prob- 

 able that the epistriatum consists properly of the cells with 

 short axis cylinders, here not fully separated from the striatum, 

 and that they receive all sensory and associational impulses 

 (e.g., from the three sources indicated above), and in turn 

 stimulate the motor cells which constitute the striatum proper. 



(3) Nuclei postolfactorii. The nucleus postolfactorius ven- 

 tralis, occupying the ventro-median angle of the fore-brain at 

 its extreme anterior end, is made up of multipolar and bipolar 

 cells. The multipolar cells measure 12 to 1 6 by 1 6 to 26 /JL. 

 They have irregularly spreading dendrites. From the cell body 

 arises a^nedium-sized smooth axis cylinder which is directed 

 backward along the ventral surface of the fore-brain, near the 

 median line. The bipolar cells have bodies measuring 16 to 

 17 by 1 6 to 32 /Ji. From each end of the cell arises a thick 

 dendrite directed parallel with the long axis of the brain. The 

 dendrites give off several small branches at right angles. The 

 posteriorly directed dendrite gradually becomes transformed 

 into a thick, varicose axis cylinder, which I have traced more 

 than half the length of the fore-brain. The axis cylinders of 

 both multipolar and bipolar cells traverse the length of the 

 fore-brain, forming a small bundle at each side of the mid- 

 ventral line, pass among the cells surrounding the recessus 

 praeopticus, and pierce the large bundles of the optic nerve. I 

 have not yet certainly determined their place of ending (Fig. 4, 

 B}. The fibers which enter and end in this nucleus come from 

 the olfactory lobe. Most or all of them are fibers which run 

 close over the central cavity; hence, probably, the axis cylin- 



