Fig. 4.

(A,B) Developmental stage: 820 day°. Neighbouring transverse sections of the lateral part of the notochord with adjacent musculature (lateral side up). (A) Alkaline phosphatase histochemistry. A thin layer of osteoid (arrow) has been deposited on the surface of the notochord, external to the elastic membrane (white arrowhead) and the chordacentrum (chc). The osteoblasts external to the notochord express ALP activity (black arrowhead). ALP staining is also present within the chordoblast layer (cb). (B) Neighbouring section stained with toluidine blue. A layer of osteoid (arrow) is present between the osteoblasts (black arrowhead) and the external elastic membrane of the notochord (white arrowhead). The chordoblast layer (cb) and the chordacentrum (chc) are indicated. Scale bars: 50 µm.