From the 5^th week (stage 15) a striking increase in volume of the cerebral vesicles (prospective hemispheres) occurs.

• Development of the cerebral cortex through immigration of neuroblasts from the ventricular zone into the marginal zone
• Development of the inner nucleus region through an accumulation of the neuroblasts in the ventricular zone of the subpallium (ganglionic eminence)

Accelerated growth of the cerebral vesicles toward the end of the embryonic phase. Out of the arch-shaped expansion results the rostroventral opened horseshoe form of the hemispheres of the telencephalon

• Appearance of the temporal lobes and of the lateral sulcus
• As a result of their more limited growth, the insula becomes covered over by the neighboring cerebral area
• Lateral ventricle and paraventricular structures (caudate nucleus, choroid plexus, fornix) follow the arch-shaped expansion of the hemisphere vesicles
• The telencephalon gradually grows around the brainstem

Development of the ganglionic eminences

• The lateral ganglionic eminence (telencephalon) develops into the neostriatum that comprises the caudate nucleus and the putamen
• The medial ganglionic eminence (diencephalon) yields the pallidum (globus pallidus) of the palaeostriatum that, descriptively, is put together with the putamen as the lenticular nucleus
• The amygdala (corpus amygdaloideum) that lies below the lenticular nucleus represents the archistriatum and should develop out of portions of the telencephalon and diencephalon

Development of the commissure and the association pathways

• The commissures of the telencephalon (corpus callosum, anterior commissure, commissure of fornix) develop out of the lamina terminalis
• The commissures of the diencephalon comprise the habenular commissure and the posterior commissure