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is now entirely given up to the olfactory apparatus, becomes 
closely associated by numerous fibre strands with the earliest 
parts of the cerebrum to appear—the tuberculum olfactorium, 
the corpus striatum, the pyriform and hippocampus. 
Thus, just as the earliest psychical life—if such an expression 
may be used—is largely influenced by olfactory impressions, so 
the early morphology of the cerebrum is dominated to a large 
extent by the olfactory apparatus. 
LATERAL VENTRICLE. 
The lateral ventricle is a narrow slit-like cavity, with a de- 
scending posterior and a descending anterior horn, of which the 
olfactory ventricle is a diverticulum. Projecting into the ven- 
tricle in the whole of its extent is the large hippocampus major 
(figs. 4 and 5, h.) on its inner wall. This is of a white color, owing 
to its coating of alveus fibres. The inner wall of the anterior part 
and of the anterior horn is largely formed by a prominent grey 
‘mass, which is the combined “septum lucidum” and precommis- 
sural area. The roof and upper part of the lateral wall is formed 
by the corona radiata (figs. 4 and 5, er.). The floor and lower 
part of the lateral wall is formed by the grey mass of the 
corpus striatum. 
The degree of bending of the lateral ventricle is one of the 
features by which the Monotreme is distinguished from the Mar- 
supial cerebrum. Thus in Wotoryctes the bend of the ventricle to 
form a descending horn posteriorly is more extensive than that 
found in Echidna, and much greater than that found in 
Ornithorhynchus, in spite of the much higher pallial development 
of both Prototheria.* 
THE CorRPUS STRIATUM. 
The corpus striatum forms a plump elongated grey mass which 
projects into the lateral ventricle and extends into its descending 
horn. It is separated from the cortex externally by a thin layer 
of medullated fibres, which constitutes the corona radiata (fig. 5, 
cr.). In the greater part of its extent the corona radiata 
forms a kind of shell (fig. 4), which supports the corpus striatum. 
In front of the anterior commissure the corpus striatum extends 
into the tuberculum olfactorium with which it is closely connected ; 
hence the name which Ganser applied to the latter structure (13). 
Behind the anterior commissure the grey matter of the corpus 
striatum is directly connected with the cortex of the pyriform 
lobe, the connecting bridge being the nuclews amygdale (fig. 5, 
n.a.). Throughout its whole length the corpus striatum is divided 
* See supplementary note. 
