Hindlimb Skeletal Structure of the Green-winged Macaw: An Anatomical Study

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In birds, the forelimb bones undergo modification to facilitate muscle attachment for flight, enabling the movement of wings up and down. Conversely, hindlimb bones primarily support walking and perching functions, necessitating evolutionary adaptations in their structure. Therefore, this study aims to document the gross anatomical features of hind limb bones in Green-winged Macaws, including the femur, tibio-tarsus, tarsometatarsus, and digits. The bones were sourced from six Green-winged Macaw carcasses undergoing post-mortem examination at the Department of Veterinary Pathology, Madras Veterinary College, Chennai. Preparation was conducted using the wet maceration technique. In the femur, the proximal end displayed a large, well-defined spherical head medially, accompanied by a small depression called the fovea capitis, and a distinct neck. The tibio-tarsus exhibited a small roughened area on its lateral border for fibula attachment, with a larger medial and smaller lateral condyle at the proximal extremity, along with a linear cinemal crest along the medial border. The fibula's distal extremity tapered into a free point, articulating at the caudolateral aspect of the tarsometatarsus. The tarsometatarsus displayed fused distal tarsals with metatarsals II, III, and IV, while Metatarsus I remained a separate bone, forming the base of the first toe. The proximal extremity of the tarsometatarsus featured two large concave articular facets for condyles from the distal extremity of the tibio-tarsus, and a facet for the distal end of the fibula caudolaterally. The Macaw's hind limb consisted of four digits, forming a zygodactyl foot arrangement.