mesocardium

Updated: May 4, 2025

A thin membrane, standing vertically in the middle plane, the mesocardium, connects the ventral wall of the head-gut with the lower head-wall. These cavities afterwards join and form the simple pericardial cavity, and are therefore called by Kolliker the "primitive pericardial cavities."

Ernst Heinrich Philipp August Haeckel - The Evolution of Man — Volume 2