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Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.
 
septum, the sinus septum, grows from the posterior wall of the sinus venosus to fuse with the valve and divide it into two parts—an upper, the valve of the inferior vena cava, and a lower, the valve of the coronary sinus (Fig. 468). The extreme upper portion of the right venous valve, together with the septum spurium, form the crista terminalis already mentioned. The upper and middle thirds of the left venous valve disappear; the lower third is continued into the spina vestibuli, and later fuses with the septum secundum of the atria and takes part in the formation of the limbus fossæ ovalis.


FIG. 466– Heart showing expansion of the atria. (Drawn from Ecker-Zeigler model.) (See enlarged image)



FIG. 467– Interior of dorsal half of heart of human embryo of about thirty-five days. (From model by His.) (See enlarged image)

  The atrial canal is at first a short straight tube connecting the atrial with the ventricular portion of the heart, but its growth is relatively slow, and it becomes overlapped by the atria and ventricles so that its position on the surface of the heart is indicated only by an annular constriction (Fig. 466). Its lumen is reduced to a

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