Blood vessels are critical in development, in normal body function, and in pathology. This image shows a branching vessel in the head of an embryonic mouse. A dye was injected into the heart and allowed to perfuse through the vessels. This technique can be used to determine where blood is being delivered in both normal growth and in vascularized tumors. At the center of this images is a branch point of the vessel, which allows blood to flow in multiple directions. Understanding the branching of vessels, and how branching is controlled, are of great interest in studying vascular biology