The Thai Journal of Veterinary Medicine


The pygmy killer whale (Feresa attenuata) is the smallest killer whale similar in size to dolphins. This mammal lives deep down in warm sea far from the shore and avoids human contact. Since the number of pygmy killer whales are gradually decreasing it could become an endangered species so it’s morphological study is an important to provide fundamental data for future study and research. The heart of a male pygmy killer whale found in the Petchaburi province of Thailand was studied anatomically. It was triangular-in shape with flattened sides being, short and wide, with a pointed apex. Subepicardial fat was not abundant. The blood supply to the heart was a bilateral coronary type of arrangement where the left coronary artery gave rise to a circumflex branch and a paraconal interventricular branch, while the right coronary artery gave rise to a circumflex branch and a subsinuosal interventricular branch. Paraconal and subsinuosal interventricular grooves appeared almost halfway between the cranial and caudal borders of the heart and ran directly to the apex. The heart was divided into 4 chambers including the right atrium, left atrium, right ventricle and left ventricle. The aortic arch gave rise to 3 arterial branches. Each cranial and caudal vena cava opened into the right atrium. Both atria were large with the right auricle having smooth edge and surface, while the left auricle had a rough edge and surface. The oval fossa, pectinate muscles and the terminal crest were found in the right atrium but an intervenous tubercle did not appear to exist. Three pulmonary valves and three aortic valves were found at the origin of the pulmonary trunk and the aorta consecutively. Trabeculae carneae, trabeculae septomarginalis, papillary muscles, chordae tendineae and atrioventricular valves were found in the ventricles, similar to those found in other mammals. This study showed that the heart of a pygmy killer whale possesses several structures similar to those of other mammals, but with a peculiar side-flattened shape and large atria. The branching pattern of the coronary arteries is the same as in the horse and pig, while the aortic arch branching pattern is similar to the human.



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