Fig. 7.

Turtle carapace. (A) Trachemys scripta (Cryptodira, Extant). Dorsal view of the cranial portion of a subadult carapace. As for most turtles, the carapace of T. scripta is composed of a complex of dermal (thecal) elements, ribs, and vertebrae. (B,C) Chelydra serpentina embryos (Cryptodira, Extant), serially sectioned. (B) Yntema stage 16, stained with Celestine blue and Direct red (the Hall-Brunt Quadruple stain). Cells of the carapacial ridge synthesize fibroblast growth factors, attracting the developing rib and drawing it into the future dermis (indicated by black arrow heads). (C) Yntema stage 22, stained with Mallory's trichrome. The developing rib is now firmly invested within the dermis. Note the development of an intramembranously derived bony spicule (black arrows). The adjacent rib is undergoing perichondral ossification. co (costal bone), cr (carapacial ridge), ne (neural bone), nu (nuchal bone), pe (peripheral bone), ri (rib). Scale bars: A = 10 mm, B = 500 µm, C = 400 µm.