The position of the nutrient foramen in the growing tibia and femur of the rat.

In rats of 40, 49 and 59 days of age the positions of the femoral and tibial nutrient foramina were determined by direct measurement, using a travelling microscope. The femoral nutrient foramen remained constant in position with increasing age, whereas the tibial nutrient foramen moved relatively nearer to the distal end of the shaft. In the case of the femur this can be accounted for entirely by differences in growth rates at the epiphyseal plates of the femur compensating for the disproportion in the distances of the foramen from the two plates. In the tibia, however, extension of the extremely oblique nutrient canal as the bone increases in girth is also involved. Bone remodelling in the vicinity of the canal is not necessary to explain the results.