Figure 4. – Histological cross sections of Russian tetrapodomorph scale material. A: Lamprotolepis ('Osteolepiformes'), fragment of a scale ornamented with dentine tubercles. B: Inset of a tubercle (odontode). Note the absence of a pore-canal system and of enamel capping the dentine tubercle. The odontodes lie on a thin and irregularly developed layer of vascular bone (spongiosa). The basal lamellar bone layer (isopedine) is thick and well developed. C: Thysanolepis (?Rhizodontida), upper portion of a scale in cross section. Note the presence of cosmine formed by the association of enamel and dentine pervaded by a pore-canal system. The middle vascular bone layer (spongiosa) is well developed and rests on the basal layer of lamellar bone (isopedine). D: Megistolepis ('Osteolepiformes'), upper portion of a scale in cross section. Note the presence cosmine and a well developed and cancellous spongiosa. The inferior part of the pore-canal system of the cosmine prolongs itself into the vascular canals of the spongiosa. Basal bony layer not visible. Abbreviations: d, dentine; e, enamel; lb, lamellar bone; mc, mesh canal; pc, pore cavity; vb, vascular bone; vc, vascular canal. Pictures courtesy of François Meunier. Scale bars: A = 1 mm; B = 500 μm; C, D = 100 μm.