Fig. 6.

Schematic illustration of the individual layers of the vertebra, shown in transverse section. The chordacentrum is in red, the autocentrum in blue and the arcocentrum in yellow. The neural and haemal arch cartilages are indicated. (A) Figure based on Arratia et al. (2001, figs 37G and 40A), illustrating the structural organization of the vertebral body components in a salmonid. In this model the autocentrum includes both the compact lamellar bone of the amphicoel and the ornamented surface of cancellous bone. It is interesting to note that layer 2 is not included. (B) Interpretation of our data in relation to A. The main differences are the presence of layer 2, which is in green, and that the autocentrum only comprises lamellar compact bone of the amphicoel. Thus, in this model, the arcocentrum reaches around the entire vertebral body, and includes the bone of the neural and haemal arches together with the external cancellous bone layer.