The brain of Acipenser. 141 
are richly branched and free from spiny roughness. The cells in 
the ventral nucleus measure 12—16 by 16—26 u, those in the lateral 
nucleus 16—20 by 20—24 u. The neurites arise in both nuclei 
usually from the cell bodies and all are destined to the ‘tween brain. 
Most of them go to the hypothalamus, but the neurites from the 
nuclei run in separate bundles of the tractus strio-thalamicus. The 
neurites from the ventral nucleus form a well defined bundle on the 
ventral surface of the fore brain at either side of the middle line 
which I shall describe below as the tractus strio-thalamicus ventralis. 
The lateral nucleus sends its neurite along the lateral surface of the 
fore brain in the tractus strio-thalamicus lateralis, to be described 
below. A part of the neurites from both these nuclei run dorso- 
caudally through the striatum and epistriatum and help to form the 
bundles to the ganglia habenulae which will be described below 
under the name of the tractus olfacto-habenularis. 
The fibres which end in these nuclei come from the olfactory 
lobe. A part of the fibres of the broad and indefinite olfactory tract 
break up here, the fibres which enter the ventral nucleus coming 
for the most part close along the central cavity, those to the lateral 
nucleus taking a more direct course. These will be more fully de- 
scribed below (page 152). 
The third olfactory nucleus is of much greater extent than those 
just described. It consists of those cells of somewhat peculiar 
