Osteohistology of the mid-diaphyseal fibula of <i>Tenontosaurus</i> in a juvenile (A,B) and two subadults (C–F).

<p>The cross-sectional geometry of the fibula changes from round to a flattened oval ontogenetically. <b>A.</b> Cross-section of OMNH 34785. This bone was invaded by bacteria before fossilization and thus much of the primary tissue is obscured. It is presented here in cross-section to illustrate vascular density and arrangement. <b>B.</b> Detail of the periosteal region of A. Longitudinal primary osteons and simple canals are visible in the periosteal region, but they do not show high levels of vascular connectivity.. The bone tissue is woven. <b>C.</b> Cross-section of OMNH 34783. This specimen was treated with oil before photography to increase light penetration, but this reduces the appearance of some thin, mineralized structures (LAGs, cement lines). <b>D.</b> Detail of the midcortex of C, showing the primary tissue of the midcortex. Most canals are longitudinal primary osteons which may show short anastomoses with one or two other canals. One secondary osteon is visible at the top of this image. A single LAG (arrow) is shown. <b>E.</b> Cross-section of OMNH 16563. <b>F.</b> Detail of the midcortex of E. As in D, canals are mostly longitudinal primary osteons. The weakly-woven bone is easier to ascertain in this image, based on the level of osteocyte disorganization. Scale bars: A = 2 mm; B,D,F = 0.5 mm; C,E = 5 mm.