The study of fourteen limbs of adult human beings by various techniques yielded the following description of the tibial blood supply. The epiphyseal-metaphyseal regions are generously supplied by vessels entering from the periphery. These vessels anastomose with vessels from the diaphyseal area. The nutrient artery is the main source of blood to the diaphyses. It gives off ascending branches immediately after it enters the medullary cavity, and these branches disperse widely. The descending branch, on the other hand, remains as a single major vessel for some distance before finally dividing. The ascending and descending branches of the nutrient artery give off radial twigs that enter the cortex. These small arteries supply the vessels of the Haversian systems. The periosteum has a copious vascular bed that contributes only infrequent capillaries to the vascular system of the cortex. Some of these capillaries traverse the cortex from periosteum to endosteum and probably represent anastomotic links with the branches of the nutrient artery. An additional anastomosis consists of the vessels in the secondary Haversian canals, as described by Ham. The venous drainage of the diaphysis is largely toward the endosteal surface through veins that accompany the arteries. At irregular intervals, however, venous channels also drain to the periosteal surface. The venous drainage of the epiphyseal region is by way of vessels adjoining the radially arranged arteries.