The medial papillary muscle complex and its related septomarginal trabeculation. A normal anatomical study on human hearts.

The morphology of the medial papillary muscle complex of the right ventricle was studied in 81 normal hearts from subjects ranging in age from 20 weeks of gestation to 13 months. The position of the main medial papillary muscle (of Lancisi) was differentiated in terms of a root and a belly. The anterior aspect of the root was found in a constant position at the basal bifurcation of the septomarginal trabeculation, whereas its belly showed considerable positional variation. Three groups of minor papillary muscles were identified and localised in specific areas in the base of the right ventricle. Taken overall, they formed part of the medial papillary complex. The complex itself was found to be constantly related to the antero-septal commissure of the tricuspid valve. A separate group of septal papillary muscles could be differentiated from the medial papillary complex. The anchorage of the septal leaflet of the tricuspid valve to the ventricular septum was also studied. The antero-superior and postero-inferior portions of this leaflet were found to be supported by the medial and posterior papillary complexes, respectively. Its midportion was connected to the septal group of papillary muscles but much variability was evident. The portion of the septomarginal trabeculation supporting the medial papillary complex, namely the postero-basal division, was studied further. This showed considerable variability and did not form a continuous anatomical spectrum.