We find in the construction of the ventral wall precisely the same processes as in the formation of the dorsal wall (Figure 1.137 B, Figure 1.144 hp, Figure 1.146 bh). It is formed on the flat embryonic shield of the amniotes from the upper plates of the parietal zone. The right and left parietal plates bend downwards towards each other, and grow round the gut in the same way as the gut itself closes. The outer part of the lateral plates forms the ventral wall or the lower wall of the body, the two lateral plates bending considerably on the inner side of the amniotic fold, and growing towards each other from right and left. While the alimentary canal is closing, the body-wall also closes on all sides. Hence the ventral wall, which encloses the whole ventral cavity below, consists of two parts, two lateral plates that bend towards each other. These approach each other all along, and at last meet at the navel. We ought, therefore, really to distinguish two navels, an inner and an outer one. The internal or intestinal navel is the definitive point of the closing of the gut wall, which puts an end to the open communication between the ventral cavity and the cavity of the yelk-sac (Figure 1.105). The external navel in the skin is the definitive point of the closing of the ventral wall; this is visible in the developed body as a small depression. (FIGURE 1.147. Median longitudinal section of the embryo of a chick (fifth day of incubation), seen from the right side (head to the right, tail to the left). Dorsal body dark, with convex outline. d gut, o mouth, a anus, l lungs, h liver, g mesentery, v auricle of the heart, k ventricle of the heart, b arch of the arteries, t aorta, c yelk-sac, m vitelline (yelk) duct, u allantois, r pedicle (stalk) of the allantois, n amnion, w amniotic cavity, s serous membrane. (From Baer.))