[Comparative morphology of the trabecula septomarginalis in terrestrial mammals]

The authors studied macroscopic morphology and histologic structure of the moderator band - trabecula septomarginalis - in 100 earthly mammals. A real trabecula septomarginalis was never found in carnivora (dog and fox) because the "anterior" papillary muscle of the right ventricle is located on the lower part of the septum ventriculorum or at times bridge-shaped above the anteiror interventricular groove and attached on both septum and anterior wall of the right ventricle. On the opposite, in ungulates, a well-known band runs across the right ventricular chamber from the septum close to the musculus papillaris coni arteriosi up to the anterior wall close to the anterior papillary muscle. In fact the attachments lie more or less approximate to the pillars; in suidae, the trabecula usually ends on a vertical trabecula carnea just under Luschka's muscle. Three types of trabecula septomarginalis were encountered as previously described by Bortolami in ox: - Mostly (66%), the trabecula septomarginalis is a short and thick fleshy column. The ratio Length mm Thickness mm amounts to about 4 to 7 and can be regarded as reasonably constant within each variety. Moreover the quotients Length mm Height of septum MM. and Thickness of the trabecula mm Highest thickness of the anterior wall mm (measured just beneath the tricuspid attachment) keep constant in each group; thus it may be concluded that size and shape of the trabecula depend on the volume of the heart and the age of the animal. - Rarely, the trabecula looks like a tendinous cord. Such a fibrous string is nearly constant in suidae, especially in wild boar, but seldom in bovidae and cervidae. In all cases, the trabecula septomarginalis supports the right branch of the atrioventricular bundle and a thin artery which originates from the left coronary artery and branches into the right coronary vessels within the anterior papillary muscle. Some venous capillaries were also observed but only in the muscular trabeculae; they are not constant and mouth into the right ventricular chamber or run towards the septal veins around the atrioventricular node. Therefore whatever is the size, the trabecula septomarginalis must be regarded as the shortest pathway from the septum to the anteiror wall of the right ventricle and is a mere band bearing the "right nodal pedicle".