After 8 days of recovery, the bone marrow was enriched in mature MK that were sometimes to be seen crossing through the endothelial barrier. (a) This MK has a highly deformed shape with half of the nucleus and cytoplasm inside the bone marrow and the other part in the vascular sinus delimited by endothelial cells. There is a zone of strangulation due to the small aperture of the endothelial barrier. In the vascular compartment, the cytoplasm is fragmented into proplatelet fragments on which constrictions (arrowheads) seem to delineate the platelet territories. (b) The cartoon schematizes the high capacity for shape deformation of the MK crossing through a very small aperture of the endothelial barrier. Bars = 5 μm.