The anatomy, ultrastructure and fluid dynamics of the developing vasculature of the embryonic chick wing bud

The spatiotemporal sequence of vascular pattern development in the embryonic chick wing bud and surrounding shoulder, flank and belly regions is detailed for Hamburger-Hamilton (1951) stages 20-25. Vasculature was microinjected with an unreactive aqueous tracer (aniline blue), and major traffic patterns were visualized. Formation of extensive avascular regions and the emergence of chondrogenic phenotypes are correlated with the retreat of the vasculature from the wing core. Ultrastructural studies of vascular cells show that vessels remain monolayered and undifferentiated until stage 25, after the adult vascular pattern has been laid down. Vascular cytodifferentiation occurs only in the cells of the brachial artery until stage 35, with the veins and capillaries retaining an 'early' morphology. This vascular pattern may be an important component reflecting or directing limb pattern development.