Vasculogenesis and chondrogenesis in the chick wing bud.

Stage 22 to stage 24 chick wing buds were labeled with sulphate-35 to identify chondrogenic areas; these areas were then related to the presence of blood vessels. Blood vessels were found in areas of increased sulphate uptake, indicating that there is no avascular area formed in the limb bud mesenchyme prior to the onset of chondrogenesis, as indicated by increased sulphate-35 uptake. It is, therefore, unlikely that the vasculature plays an initial role in the determination of chondrogenic areas in the wing bud.