196 G. ELLIOT SMITH. 
to explain the position of the thalamus in this specimen. 
Hither the hemisphere brain develops from the lateral aspect 
of the brain-tube on the ventral side of the anterior extremity 
of the thalamus, or the latter in its growth invades the Deck- 
platte. All the appearances, both in this brain and in those 
of all the Perameles and Macropus specimens, are against 
the latter hypothesis. It would appear that the hemisphere 
develops on the ventral side of the anterior extremity of the 
thalamus.) The lateral walls of the paraphysis in this speci- 
men look deceptively like anterior extensions of the Fliigel- 
platten. 
Taken as a whole, however, the general disposition of parts 
in the brain under consideration can be harmonised with the 
account of His. On tracing the pars subthalamica (Forel) or 
hypothalamus (Waldeyer) forwards in the series of sections, it 
will be found to become continuous with a large mass lying on 
the mesial side of the corpus striatum and on the ventral side 
of the optic thalamus. This mass (fig. 11, *), which forms 
the lateral wall of the ventral part of the third ventricle, on 
being traced forwards will be found (fig. 10) to become con- 
tinuous with the lamina infra-neuroporica. What is this mass? 
According to the hypotheses of Burckhardt and v. Kupffer it 
must be considered simply as the anterior extremity of the 
Grundplatte ; whereas, according to His, it must be the anterior 
end of the Fitigelplatte which has become bent towards the 
base of the brain. In fig. 11 the fibres of the external capsule 
(c. e.) will be seen extending into the mass to cross the middle 
line (fig. 10) in the lamina infra-neuroporica, so that the mass 
in question is divided into two parts—a ventral, which in the 
adult is easily recognised as the tuberculum olfactorium ; and 
a dorsal, which in the adult is corpus striatum. In the adult 
the anterior extremity of the optic thalamus fuses with the 
lamina infra-neuroporica (‘septum pellucidum”) above the 
anterior commissure, so that the combined mass appears to 
rest upon the anterior commissure. It is almost impossible 
1 Without earlier developmental stages no opinion can be expressed con- 
cerning these questions (25th April, 1896). 
