The Extraembryonic Membranes 1. In pigs it is large and important 4. Pacemaker is in sinus venosus. Formation of Heart Chambers Formation of Blood Vessels 1. Three constraints on how blood vessels are constructed physiological evolutionary physical 2.
Endothelial cells grow and divide toward organ-forming regions secreting angiogenesis factors .
Arches vestiges of the evolution of development as they in part represent the respiratory circulatory circuit of a fish's gills.