Lymph vessels of the rabbit heart: distribution and fine structure in atria

The distribution and fine structure of lymph capillaries in the atria of the rabbit heart were examined. A lymph capillary network extends into both the right and left atria but its distribution is not uniform. It is developed in the subepicardium but not in the myocardium and subendocardium of the atrial wall; overall it is less extensive than the corresponding network in the ventricles. In the atrial conduction system and in particular the sino-atrial node and the crista terminalis, the lymph network is more widely distributed; small lymph capillaries are also detected between the myocardial cells of the conduction system. A large lymph channel consistently runs along the medial side of the crista terminalis. The morphologic characteristics of atrial lymph capillaries include irregular shape, thinness of the endothelial wall, superimpositions and interlockings of the cells in the contact areas with complex junctional processes, thin and discontinuous basal membrane.