anatomical structure which has as its direct parts two or more types of tissue and is continuous with one or more anatomical structures likewise constituted by two or more portions of tissues distinct from those of their complement. Examples: osteon, cortical bone, neck of femur, bronchopulmonary segment, left lobe of liver, anterior right side of heart, interventricular branch of left coronary artery, right atrium, mitral valve, head of pancreas.