With transparent specimens and serial sections prepared from femurs of sixty human foetuses age ranging from second embryonic month to the last, after injection of dye, the medullary blood vessel construction and canals of cartilage in the femur have been studied and the following are the results. 1. At the time when bone marrow starts to grow, the vascular mesenchymal tissue enters from several places of the bone collar. The time is about the middle of the third embryonic month. 2. The site of nutrient foramen is located on the posterior surface of the long bone occupying one third of the center. In most cases two nutrient arteries are found in a femur, generally accompanied by nutrient veins. 3. Arterial branches in bone marrow during the first half of foetal life run more or less in straight line whereas during the latter half they run in undulating formation. These arterial branches are seen anastomosing with one another. 4. The venous system in bone marrow is consisted of main venous sinuses and venous meshworks connecting with them. 5. In the latter half of foetal life when there are two nutrient arteries in a femur, their branches are anast omosed with one another. 6. Metaphyseal vessels appear in the latter half of foetal life and these metaphyseal arteries are anastomosed with branches of diaphyseal arteries. 7. Canals of cartilage can be seen entering into proximal and distal epiphysis from the beginning of the fourth embryonic month. 8. In the last month of foetal life an ossification center can be recognized in the distal epiphysis, and a part of canals of cartilage is connected with the ossification center.