144 J. B. JOHNSTON, 
the fore brain. Their superficial position and the disposition of 
their processes parallel with the surface, at once give the impression 
that they belong to a special category. There are also cells at the 
extreme dorso-lateral angle of the striatum, at the point of attach- 
ment of the plexus choroideus, which are to be reckoned in this 
category. Two of these together with some epistriatum cells are 
shown in Phot. 78. The cortex cells have their bases at the sur- 
face and their dendrites directed inward. The bodies of these cells 
present a very rudimentary condition, one end of the cell being 
flattened against the limiting membrane. They may be compared 
whith the cells in the nucleus taeniae and elsewhere which have 
central processes reaching the cavity. The neurite of one of these 
cells can be followed in a sinuous course to the right hand lower 
corner of the photograph, where it continues ventrad in an extreme | 
superficial position. 
In addition to these cells on the lateral surface of the fore 
brain, I have found in several series undoubted nerve elements in 
the choroid roof. These are mostly isolated fragments of nerve 
fibres which are impregnated in several preparations. In one case 
only I have found a cell impregnated and the presence of a cha- 
racteristic neurite of sufficient length to be determined beyond a 
doubt, makes it certain that the cell is a nerve cell. In its vicinity 
were several fibres running through several sections. The appearance 
of these fibres leaves no doubt whatever that they are nerve fibres. 
Nearly all the elements impregnated are in the cephalic part of the 
plexus, dorsal to the base of the olfactory lobes. In one case a small 
bundle of fibres were impregnated and could be traced down near 
the middle line to the base of the fore brain at its junction with 
the olfactory lobes. These fibres start caudally near the middle line 
but are soon lost, so that their relations could not be determined. 
b) Fibre tracts. 
1. Tractus strio-thalamicus. This tract consists of ascending 
fibres. In Acipenser it is divided into three bundles, median, ventral 
and lateral. The ascending fibres run in the median and ventral 
bundles. The ventral bundle is made up chiefly of fibres which 
arise in the nucleus postolfactorius ventralis and run caudad at 
either side of the mid-ventral line. The fibres run ventral to, or 
through the ventral part of, the commissura anterior, pass through the 
wall of the recessus praeopticus where the bundle is augmented by 
