202 G. ELLIOT SMITH. 
concavity of the external capsule (c.e.).Anteriorly it is 
directly continued into the tuberculum olfactorium (figs. 7 
and 8), which Ganser calls the “ cortex of the head of the 
corpus striatum.” Posteriorly it is closely connected with 
the pyriform lobe (figs. 12 
14) through the intermediation 
of the nucleus amygdale. Except in the one region imme- 
diately behind the foramen of Monro (fig. 11), there is no sign . 
of any division into caudate and lenticular nuclei by an in- 
ternal capsule. 
Histologically the rudiment of the corpus striatum presents 
numerous well-formed neuroblasts, which give rise to nerve- 
fibres, whose connections will be described immediately. 
The optic thalamus presents in all sections a large mass of 
neuroblasts, which varies in size and appearance in different 
sections (figs. 1O—13). The only other structure yet differ- 
entiated in the thalamic region is the ganglion habenule 
(fig. 13, G23). 
The great thalamic nucleus, which appears to cor- 
respond to the “ centre mediane de Luys ” (Lowe and Minot), 
is relatively very largely developed in this foetus, and, as may 
be seen from fig. 14, this precocious development is an indica- 
tion of the huge proportions of the adult optic thalamus, 
whose enormous growth in the lateral direction reduces 
the corpus striatum in this region to a very thin lamella 
(fiz. 14, ¢. 8.). 
Connecting the great thalamic nucleus and the corpus 
striatum there is a huge bundle of fibres (fig. 12) which stands 
out extremely clearly, since there is practically no internal 
capsule to obscure it. By means of this fibre tract, which 
apparently corresponds to Edinger’s ‘‘radiatio strio-thala- 
mica,”’! a very intimate connection is established between the 
corpus striatum and cortex cerebri (pallium) on the one hand, 
and the ‘great thalamic nucleus”? on the other. A large 
proportion of these fibres appear to arise from neuroblasts 
in the corpus striatum. Others appear to spring from the 
thalamus. 
1 Only in part. 
