Henry Gray (18251861). Anatomy of the Human Body. 1918.
FIG. 461 Diagram to illustrate the simple tubular condition of the heart. (Drawn from Ecker-Ziegler model.) (See enlarged image)
FIG. 462 Heart of human embryo of about fourteen days. (From model by His.) (See enlarged image)
FIG. 463 Heart of human embryo of about fifteen days. (Reconstruction by His.) (See enlarged image)
The sinus venosus is at first situated in the septum transversum (a layer of mesoderm in which the liver and the central tendon of the diaphragm are developed) behind the primitive atrium, and is formed by the union of the vitelline veins. The veins or ducts of Cuvier from the body of the embryo and the umbilical veins from the placenta subsequently open into it (Fig. 463). The sinus is at first place transversely, and opens by a median aperture into the primitive atrium. Soon, however, it assumes an oblique position, and becomes crescentic in form; its right half or horn increases more rapidly than the left, and the opening into the atrium now communicates with the right portion of the atrial cavity. The right horn and transverse portion of the sinus ultimately become incorporated with and form a part of the adult right atrium, the line of union between it and the auricula being indicated in the interior of the atrium by a vertical crest, the crista terminalis of His. The left horn, which ultimately receives only the left duct of Cuvier, persists as the coronary sinus (Fig. 464). The vitelline and umbilical veins are soon replaced by a single vessel, the inferior vena cava, and the three veins (inferior vena cava and right and left Cuvierian ducts) open into the dorsal aspect of the atrium by a common slit-like aperture (Fig. 465). The upper part of this aperture represents the opening of the permanent superior vena cava, the lower that of the inferior vena cava, and the intermediate part the orifice of the coronary sinus. The slit-like