A further contribution to the development of the aortopulmonary septum in rabbit embryos.

: In rabbit embryos, the bulbar spiral endocardial ridges A-1 and B-3 develop by the moulding action of the intraheart bloodstreams ininterruptedly from the ventricular extremity to the IV and VI branchial arterial arches. Cellular basophilia is stronger where the endothelium cells and the endocardial cushion tissue cells proliferate actively and, therefore, the bulbar spiral endocardial ridges fuse and form the aortopulmonary septum.