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Fig. 465. Interior of dorsal half of heart from a human embryo of about thirty days

From model by Wilhelm His (1831-1904)

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 transverse slit, and two thickenings appear, one on its dorsal and another on its ventral wall. These thickenings, or endocardial cushions (Fig. 465) as they are termed, project into the canal, and, meeting in the middle line, unite to form the septum intermedium which divides the canal into two channels, the future right and left atrioventricular orifices.

The primitive atrium grows rapidly and partially encircles the bulbus cordis; the groove against which the bulbus cordis lies is the first indication of a division into right and left atria. The cavity of the primitive atrium becomes subdivided into right and left chambers by a septum, the septum primum (Fig. 465), which grows downward into the cavity. For a time the atria communicate with each other by an opening, the ostium primum of Bom, below the free margin of the septum. This opening is closed by the union of the septum primum with the septum intermedium, and the communication between the atria is reestablished through an opening which is developed in the upper part of the septum primum; this opening is known as the foramen ovale (ostium secundum of Born) and persists until birth.


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Reference

Gray H. Anatomy of the human body. (1918) Philadelphia: Lea & Febiger.


Cite this page: Hill, M.A. (2024, May 29) Embryology Gray0465.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Gray0465.jpg

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