118 J. B. JOHNSTON, 
and crowding of the cells is increased by the fibre tracts whose 
paths lie through this region. A large part of the tractus strio- 
thalamicus traverses it longitudinally and the fibres of the postoptic 
decussation run through it transversely. So dense is the impregnation 
in all my preparations that it is difficult to find the neurites and im- 
possible to trace them for any distance. I have followed a few of 
them to the postoptic decussation and believe that at least some of 
them cross here, probably to join the crossed tract from the inferior 
lobes to the hind brain. My information is so incomplete, however, 
that I can not say whether this is the probable course of the majority 
of the fibres. The fibres which end in this nucleus are, I think 
without doubt, secondary olfactory fibres in the tractus strio-thalami- 
cus. I have been unable to find any optic fibres entering this 
nucleus, although I have sought for them with the greatest care. 
It is only its position which has led me to call this nucleus the 
corpus geniculatum, since its relations as far as I have made them 
out would indicate that it belongs to the lobi inferiores. 
3. Corpus mammillare. 
I have described the general form and relations of the corpus 
mammillare (page 69) and in a recent paragraph have mentioned that 
the mid-ventral part of the lobi inferiores is to be reckoned with 
this body. Throughout this region the cells have peculiar characters. 
The photographs which I give of these cells (Phots. 60, 63, 64) are 
taken from the cephalic portion between the lobi inferiores, where 
the structure is more favorable for photography. In the caudal wall 
of the corpus, which is much thinner the dendrites are shorter and 
the cells are more crowded. The cells are small, measuring 8—16 
by 10—22 u, stand near the central cavity and have a central pro- 
cess which reaches the cavity. The cell body is fusiform, ovoid or 
pyramidal and from the peripheral end arises a single dendrite which 
soon divides into several slender branches which diverge and reach 
the surface. The dendrites are never profusely branched and are 
very slender and smooth. The neurites arise from the basal part 
of the dendrites. They are extremely slender fibres which in part 
form bundles near the mid-ventral line and run forward in the 
tractus strio-thalamicus to the anterior commissure and through this 
to the epistriatum. The fibres from the cells in the caudal wall 
of the corpus mammillare are divided between two widely separate 
tracts. Part go by way of the median part of the tractus strio- 
