The mastication system of the southern tamandua (Tamandua tetradactyla) was examined by means of gross anatomy and three dimensional image analysis. Three-dimensional computed tomography image analysis revealed that the mandibles medio-laterally rotated during the mastication. The temporal muscle dorso-medially pull the dorsal part of the mandubular bones, and the masseter muscle latero-rostrally operates the ventro-lateral part of the mandibles. The two muscles may contribute to the opening of the mandibles to enlarge the oral cavity and to house the contractile tongue. In contrast the medial and lateral pterygoid muscles may act as a closer of the mandible to medially pulling the ventro-medial part of the mandibles. The extraordinarily specialized mastication mechanism is functionally similar to that of the giant anteater. Although the muscles of the giant anteater show a more complicated structure in the temporal and masseter muscles than those of the southern tamandua, the weight distribution rate of mastication muscles is not so different between the two species. We suggest that the morphological design of the elongated skull and the derived feeding mastication are common in both species, and that the distribution pattern of the muscle weight has not drastically changed within the evolutionary history in Vermilingua and Myrmecophagidae.