Fig. 2.

The chordacentra develop as mineralized rings within the notochord in the period from approximately 630 to 700 day°. Cranial to the left and dorsal side up. (A) X-ray microcomputed tomographic image of the chordacentra (red) and the neural and haemal arches (grey). Chordacentrum mineralization is initiated at the ventral midline of the notochordal sheath, and they pass through a ‘horseshoe’ shape finally to form complete rings. (B) A sagittal section of the ventral region of the notochord stained with toluidine blue that shows a chordacentrum (chc) with adjacent intervertebral regions (iv). The chordacentrum is situated in the outer half of the notochordal sheath. In the regions where chordacentra form, the expansion of the notochord ceases and the notochordal sheath stops growing in thickness. In the intervertebral region, collagen production is maintained, resulting in a marked thickening of the sheath. The full thickness of the notochordal sheath is indicated by double arrow lines. Chordocytes (cc), chordoblasts (cb) and the external elastic membrane (arrowhead) are indicated. Scale bars: 100 µm.