The hindlimb muscles of Rhea americana (Aves, Palaeognathae, Rheidae).

The Greater Rhea is the largest cursorial Ratitae bird native to South America. Due to its increasing importance in farming and therefore in the sustainable use of this species, a comprehensive knowledge of their anatomy is essential. The goal of this study was to provide an anatomical description of the hindlimb muscles of Rhea americana. Six adult birds of both sexes were macroscopically studied analysing the origin and insertion of thigh and shank muscles. The thigh showed the highest number of muscles, whereas the shank showed the lowest number; this feature minimizes inertia and allows achieving high stride frequencies. The muscles of the shank showed long tendons of insertion that reduce the energetic cost during running. The major muscles responsible for extension of the hip and the ankle joints were massive and robust indicating their importance for cursorial locomotion. The pelvic limb muscles of Rhea americana resemble those of other cursorial Ratitae and their features are consistent with specialization for high-speed locomotion.