Fig. 5. Spongiosa (femur). The core of the trabeculae is constituted by remnants of primary periosteal bone, labelled at the time of its original apposition: label 1 (fluorescein injection at 2 weeks) and label 2 (alizarin injection at 3 weeks) can be seen in partly resorbed primary osteons. Locally, resorption has stopped and some endosteal bone has been apposited (label 3; fluorescein injection at 4 weeks). Scale bar, 100 µm.