The Evolutionary and Embryologic Basis for the Development and Anatomy of the Cavum Veli Interpositi

FIG. Diagram demonstrating the formation of the double-layered tela choroidea (velum interpositum) of the third ventricle in the human.

1) The developing neural tube includes the forebrain (FB) which is surrounded by the pia mater (broken line).

2) and 3) The expanding vesicle of the cerebral hemisphere (HV) carries its own pia mater (b) which overlaps the pia mater (a) of the third ventricle. IF signifies intraventricular foramen.

4) A double layer of pia mater (b, a) is interposed between the two cerebral vesicles and the third ventricle (3V). E signifies ependyma.

5) The two layers of pia mater (b, a) over the third ventricle persist after connection of the hemispheres by the commissures.