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Fig. 1.37 The middle layer of the trilaminar disc, here seen (as
in Figs 1.35 and 1.36) in transverse section, grows so fast that
the cells boil out around the other two layers to form two tubes -
digestive and neural - and to surround them in two protective
cavities - the dorsal and ventral cavities. Part of the ectoderm
'escapes' to form the skin - another tube outside all the others.
Fig. 1.39 A sagittal section of the embryo through the 4th week.
The tube of intra-embryonic coelom which runs through the
embryo is divided into separate sections which 'double bag' the
heart as it folds into the chest from the transverse septum 'above'
the head. A similar process happens from the side with the lungs
in the thorax and intestines in the abdominopelvic cavity. (Adapted
from Moore and Persaud 1999.)
Fig. 1.38 In the complex origami of embryological development,
the formation of the face and upper neck is especially intricate.
One of the last folds is to bring the two halves of the palate
together, and thus this is a common area for congenital defects.
(Reproduced from Wolpert L. Oxford University Press; 1991.)
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