192 G. ELLIOT SMITH. 
differentiation of structure. Thus on the one hand it en- 
croaches upon the mesial aspect of the cerebrum, and has a 
marked influence in the production of the complicated in- 
rolling of the hippocampus; on the other hand, it tends to 
overlap the pyriform lobe, producing the rhinal (ectorhinal) 
fissure (fig. 14, fr.). 
The corpus striatum (fig. 10, ¢. s.) is a large mass, which is 
closely related ventrally to the tuberculum olfactorium and 
pyriform lobes. Below the foramen of Monro it is closely 
connected (fig. 10) with the lamina terminalis, and behind the 
foramen it is connected with the “ Anlage” of the optic 
thalamus, which lies internal and entirely dorsal toit. The 
internal capsule is a very insignificant tract, consisting of a 
few scattered fibres (fig. 11, ¢.2.), which are only to be found 
in one region. Even in the adult (vide fig. 8) it forms a very 
scattered and relatively small system, which is indicative of 
the intermediate position of Platypus between the Sauropsida, 
which have no proper internal capsule (Meyer), and the mar- 
supials, where it is a well-formed fibre tract. 
Bebind the foramen of Monro the pyriform lobe (figs. 13 
and 14, pyr.) is directly continuous with the corpus striatum 
(c. s.), the connecting bridge being the rudiment of the nucleus 
amygdalz (nx. a.), which in the foetus gives rise to an enormous 
tenia semicircularis (¢.s.), or stria terminalis, 
The foramen of Monro forms a rounded aperture situated 
upon the lateral wall of the anterior extremity (Endhirn of 
His) of the median cavity of the fore-brain, about midway 
between the roof and the floor (fig. 2, f.m.). To be more 
exact, it opens into the lateral ventricle from a small recess 
of the third ventricle’ above the lamina infra-neuroporica, 
which is bounded anteriorly by the angulus terminalis (fig. 
3, 7. n.) and lamina supra-neuroporica (/. swp.), and dorsally by 
the horizontal extension backwards of that lamina. Into the 
dorsal aspect of this recess (fig. 15, a.) and in front of the 
foramen of Monro, the paraphysis opens (par.). The foramen 
of Monro is bounded dorsally in the whole of its extent by a 
99 ¢¢ 53 ¢¢ 
1 © Ventriculus communis, ventricle of telencephalon, aula.” 
