Fig. 7

Virtual stylopodium histology of the early-diverging dromaeosaurid Microraptor. Synchrotron microtomography of the mid-diaphysis cortex sample of the D-2842 femur; note the presence of secondary osteon (orange arrow) (A). Close-up of the cortical bone (B); note avascular periosteal regions (asterisk) and a circumferential ring of the primary osteons (red arrow). Endosteal bone of the opposite sides lined up (white arrow) due to the bone collapse leaving a slit-like medullary space in between (green arrow). The collapse led to the cortical fracture (blue arrow). Abbreviations: cICL, counterpart inner circumferential line; grm, growth mark; ICL, inner circumferential line; lanvc, laminar neurovascular canal; lnvc, longitudinal neurovascular canal; osla, osteocyte lacuna; pnvc, primary neurovascular canal; pss, periosteal surface; rel, resorption line; reos, resorption line; snvc, secondary neurovascular canal. The scale bar is 500 microns