Henry Gray (1825–1861). Anatomy of the Human Body. 1918.
pages 74
| in the body-wall toward the ventral median line, thus separating the pericardium from the lateral thoracic walls (Fig. 53). The further development of the peritoneal cavity has been described with the development of the digestive tube (page 168 et seq.). |
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FIG. 57– The thoracic aspect of the diaphragm of a newly born child in which the communication between the peritoneum and pleura has not been closed on the left side; the position of the opening is marked on the right side by the spinocostal hiatus. (After Keith.) (See enlarged image) |
| 14. The Form of the Embryo at Different Stages of Its Growth |
First Week.—During this period the ovum is in the uterine tube. Having been fertilized in the upper part of the tube, it slowly passes down, undergoing segmentation, and reaches the uterus. Peters 1 described a specimen, the age of which he reckoned as from three to four days. It was imbedded in the decidua on the posterior wall of the uterus and enveloped by a decidua capsularis, the central part of which, however, consisted merely of a layer of fibrin. The ovum was in the form of a sac, the outer wall of which consisted of a layer of trophoblast; inside this was a thin layer of mesoderm composed of round, oval, and spindle-shaped cells. Numerous villous processes—some consisting of trophoblast only, others possessing a core of mesoderm—projected from the surface of the ovum into the surrounding decidua. Inside this sac the rudiment of the embryo was found in the form of a patch of ectoderm, covered by a small but completely |