Diencephalon/Telencephalon: Neural Tube Development
The structure of the early prosencephalon closely resembles the early neural
tube i.e., thick lateral walls are connected by thinner floor and roof
plates. The early prosencephalon develops an ocular cup from its
ventrolateral walls in the position of the future diencephalon.
In the 5th week, when the embryo reaches the 7 mm stage, the simple plan of
the
prosencephalon
changes; paired
telencephalic
vesicles and the
diencephalon begin to
form from the early prosencephalon; the
optic cup continues
its development. Rapid bilateral expansion of the telencephalon results in
rearward overgrowth of the diencephalon. An early separation of the
telencephalon and diencephalon occurs through a shallow
tele-diencephalic sulcus
which deepens and persists in the adult as the horizontal
transverse cerebral fissure
(filled with duplicated pia and blood vessels, called velum interpositum).
As development progresses the growing
hemispheres continue
their caudal expansion so as to cover the
mesencephalon and
rhombencephalon (cerebellum).
