Henry Gray (18251861). Anatomy of the Human Body. 1918.
FIG. 29 Diagram of a transverse section, showing the mode of formation of the amnion in the chick. The amniotic folds have nearly united in the middle line. (From Quains Anatomy.) Ectoderm, blue; mesoderm, red; entoderm and notochord, black. (See enlarged image)
FIG. 30 Fetus of about eight weeks, enclosed in the amnion. Magnified a little over two diameters. (Drawn from stereoscopic photographs lent by Prof. A. Thomson, Oxford.) (See enlarged image)
The Umbilical Cord and Body-stalk.The umbilical cord (Fig. 28) attaches the fetus to the placenta; its length at full time, as a rule, is about equal to the