Onset of revascularization in bone healing. Seven days after performing a standardized osteotomy in a sheep‘s tibia, the maturating granulation tissue clearly shows newly formed vessels (A: hematoxilin-eosin staining; 20 × magnification, B: α-SMA, methylgreen counterstaining, vessels depicted in red, 40 × magnification). For these vessels to be this highly developed, revascularization in the hematoma must have started earlier. C and D (Alcian blue staining): The importance of the revascularization becomes evident when observing the cutting edge of cortical bone (CB) where a high number of vessels developed between bone and granulation tissue remnants (GT). The density of this capillary formation is illustrated in D, where endothelial cells, indicating vessel borders, lie nearly wall to wall.