Chapter 156. The Brain: The Telencephalon (first Vesicle) – Lobes and Pallial Development - Review of Medical Embryology Book

THE TWO PRIMITIVE HEMISPHERES GROW FORWARD, producing the frontal lobes, and backward where they cover the diencephalon and form the parietal and occipital lobes. The posterior pole then expands and grows in a forward direction to form the future temporal pole

Thus, the vaults of the hemispheres take on a horseshoe shape and delimit the fossa of Sylvius (sylvian fissure), by month 9
In a parallel manner, the posterior areas continue to grow and gradually cover the mesencephalon and part of the metencephalon

The ventricular cavity sends forth a process into the temporal lobe to form the inferior horn of the lateral ventricle and another into the occipital lobe to form the posterior horn of the lateral ventricle
In the paraventricular areas of the floor plate, the caudate nucleus, which protrudes into the cavity of the lateral ventricle, follows the turning movement of the posterior pole of the hemisphere and thus becomes horseshoe-shape
The putamen rotates very little and is arched in an anteroposterior direction. It is surrounded progressively by the caudate nucleus
The central globus pallidus does not move at all
The surface of the pallium folds increasingly during its transverse and longitudinal development. Toward month 6, the parieto-occipital fissure of Rolando makes its appearanc From month 7 on, grooves form that separate various convolutions well established at birth