The families of Swifts, Nightjars, and Frogmouths, here classed together, afford an even more difficult case than that of the Anisodactyli, their differences being of so well-marked and important a character as to make it very doubtful whether they can belong to the same order. The hallux in all is connected with the flexor perforans digitorum, and the arrangement of the deep flexors (except in Macropteryx) is Galline, as in Coracias and Buceros; the oil-gland is nude or wanting, the manubrium sterni very small or absent, the coracoids separate, and the number of both primary-quills and tail-feathers 10. The spinal feather-tract is well-defined on the neck, but forked on the upper back. All, too, have a short bill and an excessively broad gape, and all live on insects captured in the air.
The three families Cypselidae, Caprimulgidae, and Podargidae form suborders.
The Trochilidae, or Humming-birds of America, are generally placed in this order, but their relations to the Swifts are disputed by a few naturalists.
Another American family, Steatornithidae, appears probably allied to the Podargidae.
The other suborders are all Indian, and may be thus distinguished :—
a. Palate aegithognathous; no basipterygoid processes ; no caeca ; a nude oil-gland……………….CYPSELI.
b. Palate schizognathous ; basipterygoid processes present; caeca functional; a nude
c. Palate desmognathous; no basipterygoid pro¬cesses ; caeca large; no oil-gland; a powder-down patch on each side of the rump……………….PODARGI.