116 _J. B. JOHNSTON, 
cerebellaris et bulbaris and become indistinguishable in that tract. 
I suppose that they enter the cerebellum but they may also go to 
the medulla. My preparations are not at all ambiguous on this point, 
and there is no evidence of the neurites taking any other course. 
I have been unable to find any indication of a crossed tract (Binde- 
arm of German authors) from the nucleus ruber to the cerebellum. 
The tract in Acipenser is a direct tractus tegmento-cerebellaris. 
It is difficult to determine what fibres find endings in this 
nucleus. Both the tractus tecto-lobaris and the tractus lobo-cerebel- 
laris et bulbaris rectus pass through it. If any fibres of either of 
these tracts end in the nucleus ruber they are difficult to recognize 
because of the enormous complication when these tracts are im- 
pregnated. Many neurites from cells of the central grey matter run 
far laterad as if they might enter this nucleus, but I have not been 
able to demonstrate their endings here. 
c) Hypothalamus. 
1. Lobi inferiores. 
The large inferior lobes of Acipenser possess a uniformity of struct- 
ure not possessed by any other part of the brain. The wall is divided 
into two zones, a cellular zone adjoining the cavity and a fibre zone 
which forms the outer four-fifths of the wall (Phot. 22). In the 
same photograph is seen at either side of the mid-ventral line a 
thickening or ridge. That part of the ventral wall mesial to these 
ridges has a structure similar to that of the corpus mammillare, with 
which it is continuous caudally, and I shall describe it as a part of 
the corpus mammillare. On the dorsal wall of the lobes where 
they become continuous with the thalamus, the characteristic structure 
of the lobes continues nearly to the angle at which the wide cavity 
of the lobes joins the narrower third ventricle proper. 
Throughout the whole extent of the lobes the cells are es- 
sentially the same (Phots. 59, 65, 69, 70), although the fibre tracts 
which enter and leave the lobes are various. The cells stand near 
the cavity and send their dendrites radially outward. The cell bodies 
are ovoid, fusiform, pear-shaped, or nearly cubical, and measure 
8—18 by 18—32 u. A single large dendrite arises from the peri- 
pheral end or apex; of the cell and divides into several branches 
which diverge as they approach the ectal surface. The dendrites 
are thickly set with fine spines which are of considerable length and 
