Fig. 6 in Carapace bone histology in the giant pleurodiran turtle Stupendemys geographicus: Phylogeny and function

Fig. 6. Bone histology of Pelomedusa subrufa (Bonnaterre, 1789); Recent, Africa (provenance unknown). Thin−section of a sampled costal (MVZ 230517). A. The whole of the thin−section observed in polarized light. The diploe build of the shell is apparent below a keratinous shield (see also Fig. 2G). Only a thin layer of connective tissue is present in between the shield tissue and the bone tissue. The plane of sectioning lies perpendicular to the incorporated rib in the costal. In the thin−section, the former rib is only seen as a dorsoventrally thickened amount of cancellous bone and the slightly curved internal cortex. B. Detail of the external cortex of the costal in polarized light where the interwoven fiber bundles are interspersed with primary osteons. Bone cell lacunae that appear within the whole of the cortical bone are rather of round shapes. C. Detail of the parallel−fibered bone of the internal cortex of the costal. Below the surface of the bone, a thin layer of fibrous connective tissue is still present. Abbreviations: CL, bone cell lacunae; CT, connective tissue; ECO, external cortex; ICO, internal cortex; ISF, interwoven structural collagenous fiber bundles; KS, keratinous shield; PFB, parallel−fibered bone; PO, primary osteon, SF, structural collagenous fiber bundles; TR, bone trabeculae.