Henry Gray (18251861). Anatomy of the Human Body. 1918.
the dorsal end of the septum transversum the lung buds come to lie above the septum and thus pleural and peritoneal portions of the pleuro-peritoneal cavity (still, however, in free communication with one another) may be recognized; the pericardial cavity opens into the pleural part.
FIG. 55 Upper part of celom of human embryo of 6.8 mm., seen from behind. (From model by Piper.) (See enlarged image)
The ultimate separation of the permanent cavities from one another is effected by the growth of a ridge of tissue on either side from the mesoderm surrounding the duct of Cuvier (Figs. 54,55). The front part of this ridge grows across and obliterates the pleuro-pericardial opening; the hinder part grows across the pleuro-peritoneal opening.
FIG. 56 Diagram of transverse section through rabbit embryo. (After Keith.) (See enlarged image)
With the continued growth of the lungs the pleural cavities are pushed forward