The Hindlimb Musculature of the Mousebirds (Coliiformes)

The hindlimbs of two species of mousebirds (Colius striatus and C. leucocephalus) were dissected in order to provide myological descriptions, to elucidate the mechanism of digit rotation and other characteristic locomotor habits, and possibly to yield clues to the systematic position of the order Coliiformes. Among the myological peculiarities, the unusually large M. iliofemoralis externus, the accessory belly of M. pubo-ischio-femoralis, and the extensive femoral insertion of M. flexor cruris lateralis and origin of M. flexor hallucis longus are features related to the hanging postures of the Coliiformes. Digit rotation is accomplished primarily by enlargement and slight changes in the insertions of four intrinsic foot muscles. Two small intrinsic foot muscles, not previously described in birds, also appear to be associated with digit rotation. In the species dissected, the extensor digitorum longus tendon sends a branch to the hallux as well as to the three forward digits. This condition has previously been described only in the Psittaciformes, and may possibly suggest a common ancestry for the two orders.