20 rats were given a certain quantity of india ink with 10% of its volume of gelatine-solution added to it by infusion through the aorta into the blood vessels of the mandibular bones, and the bones and surrounding tissue were made transparent by Spaltheholz's method for observation of the blood vessels. 1. It was found that there are three kinds of artery supplying the rat mandibular bone and teeth : the inferior alveolar artery and its molar branches passing through the accessory foramina of the alveolar processus, and mental artery. 2. The inferior alveolar artery supplies the incisor tooth and the third molar tooth and the molar branches supply the first and the second molar tooth. The mental artery supplies anterior root of the first molar tooth. These three kinds of artery have each a comitant vein. 3. Capillary anastomosis between the capillaries in the bone-marrow and those in the periodont of the molar teeth are often observed. 4. The periodont of the incisor tooth has much more vascularity than those of the molar teeth. 5. The venous drainage and vascularity of the incisor periodont are peculiar and complicated. The supeior one third of it is higher in vascularity than the middle one third, and the inferior one third, especially in its central part, has the highest vascularity. 6. There are five or six periodontal veins running parallel to the axis of the incisor tooth, one running along the superior margin, another along the inferior, two others along the lateral surface and the remaining two along the medial surface.
