Fig. 2. Formation of the vitelline artery. Time-lapse video-microscopy of a 19 ss chick embryo in New culture. Endoderm is facing up. Still images at the indicated times are shown. Note the formation of the vitelline artery (black arrows), which becomes clearly visible at the 21ss (C). Red and blue arrows indicate arterial and venous blood flow, respectively. White arrowheads indicate capillary free-zones. Asterisks show distal progression of vitelline artery formation. (H) The posterior vitelline vein (blue arrow) is formed. Scale bar: 1500 µm.