114 J. B. JOHNSTON, 
The cells cephalad from the nucleus anterior send their neurites 
into the common longitudinal bundle in the direction of the com- 
missura anterior. These cells lie too far forward, at the extreme 
cephalic border of the thalamus, to form part of the end-nucleus of 
the optic fibres. It is possible that fibres from the tectum break 
up among these cells. I know of no previous description of 
them. 
The common longitudinal bundle is entirely separate from the 
tractus olfacto-habenularis. The latter lies superficially in the dorsal 
and ectal parts of the cell mass just described, while the common 
bundle runs deep among the cells. It contains: 1) fibres which 
seem to connect the tectum with some part of the fore brain, 
2) fibres from the nucleus praetectalis into the tectum, 3) fibres 
from the cells cephalad from the nucleus anterior toward the fore 
brain, 4) fibres of unknown origin which end among the epithelial 
cells of the epiphysial sac, 5) fibres from these cells which seem to 
end in the nucleus anterior, 6) fibres of unknown source and de- 
stination which decussate in the epiphysial decussation. 
2. Central grey Matter of Thalamus. Nucleus diffusus. 
In the thalamus between the optic tracts and the nucleus ruber 
tegmenti on the one hand and the central cavity on the other are 
numerous nerve cells, either bordering on the central cavity in two 
or three layers or scattered among the various fibre tracts. In the 
cephalic part of the thalamus, ventral to the nucleus anterior, the 
cells measure 11—18 by 20—28 u. Many of these cells have central 
processes reaching the cavity, while others lie among the fibre tracts 
or have a position parallel with the inner surface. In the caudal 
part of the thalamus several cells give measurements of 12—16 by 
28—48 u. Taking a large number of measurements from all parts 
of the central grey, I find that the cells vary greatly in size, the 
figures being 10—18 by 20—64 u. 
In the ventral part of the thalamus are the cells which give 
rise to the fibres of the fasciculus longitudinalis posterior. In sagittal 
sections to one side of the median plane I have traced the neurites 
of the cells directly into the fasciculus. The nucleus is diffuse, 
extending through the ventral half of the central grey, so that the 
fasciculus at its origin spreads like a fan. 
In the extreme ventral part of the thalamus, at either side of 
the III ventricle where it widens into the cavity of the lobi in- 
