Histological features of the rank 1 pseudotooth of specimen AaO-PT-C.

<p>(A) Horizontal thin section in the apical region. Main frame: polarized transmitted light; insert: ordinary transmitted light. Remnants of primary bone tissue (asterisk) are scarce, whereas longitudinal primary and secondary (O₂) osteons are abundant and appear monorefringent. Reversion lines (rl) are clearly visible around the secondary osteons. (B) Transverse thin section in the walls of the pseudotooth. Polarized transmitted light. The osteons are brightly birefringent, which reflects the longitudinal orientation of their collagen fibers. (C) Transverse thin section in the pseudoteeth walls. Ordinary transmitted light. Osteocyte lacunae have a spindle-like morphology in the parallel-fibered bone forming the osteons. There is an artefactual wrenching at the lower right of the image. (D) Virtual horizontal slice (microtomographic) showing differences in the mineralization rate of the osteons. (E) Transverse thin section in ordinary transmitted light. Howship's lacunae (arrows) on the deep side of the wall. (F) Aspect of the basal plate viewed in a transverse thin section. Polarized (centre of the section) and ordinary (lateral parts) transmitted light. Osteons (mostly secondary) are oriented sagittally. Some superficial resorption occurred locally (arrow), whereas the deep face of the basal plate was partly reconstructed by endosteal deposits (asterisk) after resorption. (G) Longitudinal thin section. Polarized transmitted light. The osteon orientation creates a sharp distinction between the basal plate (bp) and the walls of the pseudotooth (wpt). Scale bars = 200 µm.