[Fundamental anatomy of the third ventricle].

Comparative anatomy of the third ventricle shows that this diencephalic cavity is present in most vertebrates. In humans, the roof of the third ventricle has thinned and most of its diverticles have disappeared. Human embryology underlines the development of hemispheric vesicles and interhemispheric commissures, and both of these structures progressively dissimulate the third ventricle deep within brain tissue. The anatomy of the third ventricle, particularly the roof of the ventricle and the interventricular foramen are described, with special references to their relationship with surrounding structures and vessels. The knowledge of these anatomical landmarks is essential to operative approaches to the third ventricle.