This order is distinguished from all other zygodactyle groups, except the Parrots, by possessing the ambiens muscle, a character to which a very high importance was attached by Garrod, and by the deep plantar tendons being arranged as in Gallinaceous birds, and only differing in arrangement from the Passerine plan by being .connected by a vinculum;. the flexor longus hallucis leads to the hallux alone, the flexor perforans digitorum serves the; other three digits., The palate is desmognathous; basipterygoid processes are wanting.
Two families are included—the Cuculidae and Musophagidae; the latter, however, is entirely African, and the former alone requires notice here.
By Garrod, Newton, and other recent writers, the Coccyges have been regarded as having Galline affinities. The aberrant type Opisthocomus appears to be a link between Gallinae and Musophagidae.