J. Embryol. exp. Morph. 54, 75– 98 (1979)

The Editors regret that Figures 2–6 of the above paper contained inaccuracies. The revised version of this plate is published here.

FIGURE 2–6.

Fig. 2. A scanning electron micrograph of the somitic region of stage-12 chick embryo from the point of view of the neural tube (removed). The ventralmost portion of each somite is almost vertical to the midline and represents that region which borders the notochord. In the more posterior somites, a vertical cleft is already visible in the ventral-medial portion of the somite (thin arrow). The dorsal portion of each somite is concave and reflects the expansion of the neural tube from the midline. Anteriorly, this surface of the somite is covered with neural crest cells (thick arrow). The height of the somite increases by nearly 50 % when the most recently formed and tenth somite (star) are compared, × 1480.

FIGURE 2–6.

Fig. 2. A scanning electron micrograph of the somitic region of stage-12 chick embryo from the point of view of the neural tube (removed). The ventralmost portion of each somite is almost vertical to the midline and represents that region which borders the notochord. In the more posterior somites, a vertical cleft is already visible in the ventral-medial portion of the somite (thin arrow). The dorsal portion of each somite is concave and reflects the expansion of the neural tube from the midline. Anteriorly, this surface of the somite is covered with neural crest cells (thick arrow). The height of the somite increases by nearly 50 % when the most recently formed and tenth somite (star) are compared, × 1480.

Fig. 3.

A scanning electron micrograph of the ventral-medial region of an anterior somite at stage 12 of development. Viewed medially, the sclerotome is already divided into anterior and posterior halves by the sclerotomal fissure (curved arrows). The large arrow points to an intersomitic cleft, × 470.

Fig. 3.

A scanning electron micrograph of the ventral-medial region of an anterior somite at stage 12 of development. Viewed medially, the sclerotome is already divided into anterior and posterior halves by the sclerotomal fissure (curved arrows). The large arrow points to an intersomitic cleft, × 470.

Fig. 4.

A scanning electron micrograph of the extracellular matrix accumulated between the surface ectoderm (removed) and dermamyotome at stage 12 of development. Many of the fibrillar elements, studded with granules, course along in small bands primarily in an axial direction (arrows). In transmission electron micrographs, faintly periodic fibrils, 10–15 nm in diameter, are seen. Occasionally the basal cell processes of somitic cells appear trapped in matrix, ×1390.

Fig. 4.

A scanning electron micrograph of the extracellular matrix accumulated between the surface ectoderm (removed) and dermamyotome at stage 12 of development. Many of the fibrillar elements, studded with granules, course along in small bands primarily in an axial direction (arrows). In transmission electron micrographs, faintly periodic fibrils, 10–15 nm in diameter, are seen. Occasionally the basal cell processes of somitic cells appear trapped in matrix, ×1390.

Fig. 5.

A scanning electron micrograph of the most recently formed somite, similar to that labeled ‘1’ in Fig. 1, which has been cross-fractured. Viewed medially, individual cells are bottle-shaped, tapered inward toward the somite center. The centralmost cells are less oriented and more rounded. The cells of the surface ectoderm, overlying the somite, border considerable amounts of intercellular space, creating caverns and channels throughout the epithelium, ×615.

Fig. 5.

A scanning electron micrograph of the most recently formed somite, similar to that labeled ‘1’ in Fig. 1, which has been cross-fractured. Viewed medially, individual cells are bottle-shaped, tapered inward toward the somite center. The centralmost cells are less oriented and more rounded. The cells of the surface ectoderm, overlying the somite, border considerable amounts of intercellular space, creating caverns and channels throughout the epithelium, ×615.

Fig. 6.

A transmission electron micrograph of a thin section taken through the most recently formed somite. The neural tube (n.t.) is at the upper left. The somitic wall is rather uniform in thickness and typical of pseudostratified embryonic epithelia in that mitoses occur preferentially at the lumenal (myocoele) surface (arrows), × 535.

Fig. 6.

A transmission electron micrograph of a thin section taken through the most recently formed somite. The neural tube (n.t.) is at the upper left. The somitic wall is rather uniform in thickness and typical of pseudostratified embryonic epithelia in that mitoses occur preferentially at the lumenal (myocoele) surface (arrows), × 535.