DEVELOPMENT OF THE TENDON OF TODARO DURING THE HUMAN EMBRYONIC AND FETAL PERIODS

This study covers the development of Todaro's tendon during human embr yonic and fetal periods. The tendon primordium first appears when huma n embryos attain a CR length of 22 mm, but it only becomes well-define d at 24 mm CR length. The tissue that will form the tendon proceeds ex clusively from the inferior endocardial cushion. The tendon establishe s a close relationship with the base of the septum secundum during its path towards the right venous valve, carrying myocardial tissue out a nd forming the fasciculus limbicus inferior to muscular tissue. The te n don's relationship with the superior aspect of the atrioventricular node primordium during the first part of its path is of particular int erest. 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 largel y responsible for the development of the sinus band which protrudes as a crest inside the right atrium. This band is particularly well-devel oped in the fetal heart and provides an explanation for the large sub- Eustachian sinus cavity. (C) 1994 Wiley-Liss, Inc.