Development of the tendon of todaro during the human embryonic and fetal periods

This study covers the development of Todaro's tendon during human embryonic and fetal periods. The tendon primordium first appears when human embryos attain a CR length of 22 mm, but it only becomes well-defined at 24 mm CR length. The tissue that will form the tendon proceeds exclusively from the inferior endocardial cushion. The tendon establishes a close relationship with the base of the septum secundum during its path towards the right venous valve, carrying myocardial tissue out and forming the fasciculus limbicus inferior to muscular tissue. The tendon's relationship with the superior aspect of the atrioventricular node primordium during the first part of its path is of particular interest. The relationship is most intriguing when the node morphology is least defined. This would explain the possible embryogenesis of extra atrioventricular nodes. We also consider Todaro's tendon to be largely responsible for the development of the sinus band which protrudes as a crest inside the right atrium. This band is particularly well-developed in the fetal heart and provides an explanation for the large sub-Eustachian sinus cavity. © 1994 Wiley-Liss, Inc.