Figure 4. - Scales of Obaichthys africanus (MRS 45). A-B: Cross section of two scales (transmitted natural light), showing the three superimposed layers: pluristratified ganoine (g), dentine (d) and bony basal plate (bp); A: MNHN-Histos 1960. The arrowheads point to five ridges of ganoine. The basal plate (bp) is avascular; B: MNHN-Histos 1963. The arrowheads point to three ridges of ganoine. A vascular canal (vc) crosses the whole scale; C-H: Cross sections of scales (transmitted natural light); C: MNHN-Histos 1960. Detail of A showing the two median ridges (arrowheads) constituted of pluristratified ganoine (g), each one above a dentine unit (d). The two ridges lie on an avascular bony basal plate crossed by numerous canaliculi of Williamson. Two sections of vascular canals just below the right dentine unit are visible (arrows). Notice the growth marks (gm) in the basal plate (bp); D: MNHN-Histos 1964. Detail of the ganoine layer (g) showing two odontode bases (arrows) and a resorbed area (asterisk) characterized by its irregular alveolate walls. Two minor remodelling areas (arrowheads) are seen in the ganoine layer; E: MNHN-Histos 1964. Detail of an odontode base (arrow) in the ganoine layer. One can also show two canaliculi of Williamson crossing the ganoine strata (arrowheads); F: MNHN-Histos 1964. Detail of a dentine unit (d) organized above a vascular loop coming from the basal plate (bp), with numerous odontoblastic canalicles (black asterisks). (g = ganoine); G: MNHN-Histos 1964. Detail of a dentine bulk (d) subtending a ganoine ridge (g). The odontoblastic canalicles radiating from the vascular ramification are visible. A canaliculus of Williamson (arrowhead), and some osteocytes in the bony basal plate (white asterisk) are visible; H: MNHN-Histos 1963). Detail of the bony basal plate showing a dichotomized canaliculus of Williamson (arrow). Scale bars: A, B = 1 mm; C = 250 µm; D, F = 100 µm; E = 100 µm).