Fig. 8

Virtual zeugopodium histology of the early-diverging dromaeosaurid Microraptor. Synchrotron microtomography of the mid-diaphysis cortex sample of the D-2842 tibia; note the growth mark (white arrow) versus resorption front (black arrow) (A). The close-up of the bent cortical bone shows partly resorbed primary osteon and thick endosteal bone (B). The close-up of flattened cortical bone shows three major divisions of the cortex including the endosteal bone (ICL, red column), the mid-periosteal cortex with higher vascularity (green column) and paired osteons (dashed line), and the periosteal cortex with reduced vascularity (blue column) (C). Close-up of the neighbouring cortex that exhibits an increased periosteal avascularity together with the neurovascular canal open on the bone surface (D). Abbreviations: enbo, endosteal bone; grm, rowth mark; ICL, inner circumferential line; lnvc, longitudinal neurovascular canal; meca, medullary cavity; osla, osteocyte lacuna; pnvc, primary neurovascular canals; ponvc, periosteally open neurovascular canal; pos, primary osteon; ras, radially protecting vascular anastomosis; rnvc, radial neurovascular canal; rel, resorption line; reos, partially resorbed osteon; twos, pair of two closely associated osteons. The scale bar is 500 microns