Figure 15.

These schematic drawings illustrate the centripetal growth concept of ventricular trabeculation. (A) Initial step of trabeculation. (B) Advanced step of trabeculation. According to this concept, myocardial trabeculae are formed mainly from cardiomyocytes of the inner (basal) layer of the ventricular myocardium (marked by dark red color). Recent data suggest that non-removed remnants of CJ along the outer curvature of the ventricular bend serve as pathways for inward growth of the trabeculae toward the center of the embryonic ventricle. Inward growth of myocardial trabeculae separates endocardium-lined intertrabecular spaces (it) from the free ventricular lumen. Outward growth of endocardial sprouting into the myocardial wall does not significantly contribute to the formation of intertrabecular spaces. Note that inward growth of trabeculae is expected to narrow the free lumen of the embryonic ventricles during the initial step of trabeculation. Note also that the embryonic ventricles expand (ballooning) concomitant with the growth of the trabeculae. Same color code and abbreviations as used in Figure 13.