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Fig. 7.2 Images of the germ layers from “Beiträge zur Entwickelungsgeschichte des Hühnchens
im Eye” (1817). (A) d’Alton’s drawing by of the chicken embryo showing the blood islands sur-
rounding the area pellucida of the blastoderm on top of the yolk (Tab IV). (B) d’Alton’s drawing
showing a top view of the chicken embryo, including the entire circulatory system (Tab VIII). (C)
Drawing of chicken eggs in cross section. Figure 1 shows the extent of the germ layer spreading
over the yolk during development. (a) Yolk mass; (b) the site of entry into the egg shell; (arc c–c),
endoderm, (d–d arc) mesoderm; (e) embryo, (f–f arc) ectoderm; (g) vitelline membrane; (h, i)
Chalaza; (k) egg shell. Figures 2–9 show top views (Figs. 2, 3, 5, and 6), lateral (Figs. 4 and 7) and
medial cross sections (Figs. 8 and 9) of the blastoderm at different stages. In all figures, (a) repre-
sents what Pander called the “primitive folds,” which we call today the neural folds. (b) indicates
the head folds. In Fig. 3, the line (c) indicates the point level of the cross section shown in Fig. 8.
In Fig. 6, line (d) indicates the level of the cross section shown in Fig. 9. (c) and (g) indicate the
upper and lower layers of the head fold, (f) indicates the anterior edge of the head fold. In Fig. 7,
the lines (d) and (e) show the direction in which Pander and colleagues moved the embryonic folds
with a bristle or needle (Tab der Durchschnitte). Images used with permission of Bayerische
Staatsbibliothek, Münich. urn:nbn:de:bvb:12-bsb10315830=0. Shelfmark (2 Anat 49)
W. Tseng et al.