Morphology and Histology of the Heart of the Australian Lungfish, Neoceratodus forsteri (Krefft)

Abstract

AbstractThe wall of the sinus venosus consists of densely packed collagen fibres and scattered striated muscle fibres. Striated muscle makes up the spongiosa of the auricle but is completely absent from the auricular wall, which only contains connective tissue. The lateral lobes of the auricle are small and do not reach the ventral side of the heart. The hard nucleus in the auriculo‐ventricular plug consists mainly of dense elastic tissue, not of cartilage as in the other lungfishes. The general morphology of the heart, including the entrance of the pulmonary vein, the auriculo‐ventricular plug and the spiral valve of the bulbus cordis, is similar to that of the other lungfishes, so arterial and venous blood can probably be separated in the same way in Neoceratodus up to the level of the bulbus cordis. However, Neoceratodus lacks the horizontal septum in the distal part of the bulbus and all branchial arteries are emitted from an undivided space in the short truncus arteriosus. Thus the mechanism of separation in the distal bulbus of Neoceratodus must be very different from that of the other lungfishes.