The brain of Acipenser. 139 
mid brain. The fibres are seldom impregnated and I have not found 
the cells of origin. In sagittal sections the fibres turn caudad as 
they pass ventrad and run nearly parallel with the bundles of MEY- 
NERT. A part of them are readily followed back to the level of 
the ansulate commissure, where they come into contact with the 
bundle y. It seems probable that at least a part of the fibres of 
the posterior commissure come from the ventro-lateral tracts of the 
medulla and mid brain. 
3) The epiphysial decussation has been fully described (page 108). 
4) The commissura habenularis has been described (page 110). 
E. Fore Brain. 
a) Nuclei. 
1) Corpus striatum. 
The corpus striatum constitutes the main body of the fore brain. 
It is made up of two incompletely separated nuclei, the striatum 
proper and the epistriatum. The epistriatum occupies the dorsal, 
internal part of the fore brain and in haematoxylin sections is 
characterized by numerous rows of cells whose dendrites are directed 
radially outward. The striatum lies ventrad from this and contains 
fewer cells without regular arrangement. Phots. 24, 25. 
Epistriatum. — The cells are pyramidal in form, measure 
12—26 by 16—40 u, and are arranged in several layers (four to 
twelve according to the part of the fore brain studied) parallel with 
the internal surface. The apices of the cells are directed outward 
and the bases are often in close contact (Phot. 76). Two or more 
dendrites arise from the base of the cell and spread in all directions 
between and parallel with the layers (Phot. 77). From the apex arise 
from one to four larger dendrites which diverge more or less but 
have in general a radial arrangement (Phots. 75, 79). All the 
dendrites are supplied with small knobbed spines similar to those 
on the cells in the lobus inferior (Phots. 75, 79, cf. Phot. 59). The 
neurites (Phots. 76, 79) arise either from the side or apex of the cell 
bodies or from the first part of one of the basal or apical dendrites. They 
are medium or slender, smooth fibres which run radially outward 
(latero-ventrad). The fibres are nearly parallel and are so numerous 
that they give a fine radial striation in addition to the coarser 
striation due to the dendrites. They give off collaterals (Phot. 79) 
which do not branch profusely but give rise to a few long slender 
