730 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 
=AHeterodactyle Scuater, Ibis, Oct., 1880, 401, in text.—Dusois, Mém. Soc. 
Zool. France, 1891, 115. 
=Trogonine A. MinnE-Epwarps, Ois. Foss., ii, 1867-1871. 
= Trogonoidex StEIJNEGER, Stand. Nat. Hist., iv, 1885, 433, in text. 
= Trogonoidet Copz, Am. Nat., xxiii, Oct., 1889, 872, 873. 
=Trogones AMERICAN ORNITHOLOGISTS’ Union, Check List, 1886, 208.—FuER- 
BRINGER, Unters. Morph. Syst. Vég., 1888, 1567.—SEzBoum, Classif. Birds, 
1890, pp. vii, xi, 8—Suarpz, Rev. Classif. Birds, 1891, 92; Hand-list, ii, 
1900, 146.—Gapow, in Bronn’s Thier-Reich., Vég., ii, 1893, 254, 301; Classif. 
Vertebr., 1898, pp. xv, 37..-Brpparp, Struct. and Classif. Birds, 1898, 
202.—Know1tton, Birds of the World, 1909, 50. 
Zygodactylous but heterodactylous and heteropelmous coraciiform 
birds with myological formula AX and with the dorsal pteryla simple 
(not forked) between shoulders. 
Palate schizognathous; nasals holorhinal; basipterygoid processes 
present; vomer present; metasternum 4-notched; spina interna ab- 
sent, spina externa present (long and bifid); coracoids touching but 
not connected; hypotarsus complex; cervical vertebra 15; complete 
ribs, 4-5 pairs; syrinx tracheo-bronchial; only the left carotid artery 
developed; ce#ca present (but short); intestinal convolutions of type 
VI; flexor tendons of type VIII; femoro-caudal and semitendinosus 
muscles present, the accessory femoro-caudal absent; pterylosis pas- 
serine, the spinal pteryla well defined from nape to oil-gland, not 
forked; wing-coverts coraciine (middle coverts absent); oil-gland 
nude; aftershaft of contour feathers very large; no adult downs; rec- 
trices 12; tenth (outermost) primary very short; secondaries quinto- 
cubital; young gymnopedic. 
The Heterodactyle are a strongly characterized group of Coracii- 
form birds which combine the cranial characters of the Caprimulgi, 
the myological formula of the Alcedinide (= Anisodactyle, part), and 
an oscinine pterylosis with an entirely unique arrangement of the toes 
and the deep plantar tendons. Like the Pici and Cuculiformes, they 
have the toes in pairs (two in front and two behind), and are therefore 
to that extent zygodactylous; but they differ from these two groups 
and from all other birds in having the second digit (the inner front toe 
of anisodactyle birds) reversed, instead of the outer toe; in other 
words, the hallux is the outer of the two hind toes, whereas in all other 
zygodactyle birds it is the inner one. This unique arrangement of 
the toes is correlated with a unique arrangement of the deep plantar 
tendons, the front one of which (the flexor perforans) is split into two, 
leading, respectively, to the two front (third and fourth) toes, while 
the hinder one (the flexor hallucis) is also divided, the two branches 
leading, respectively, to the two posterior (first and second) toes—an 
arrangement in strong contrast with those of the other zygodactyle 
groups, in which the front plantar leads to the third digit only in the 
Pici, while the hind plantar leads to the first digit (hallux) only in the 
Cuculiformes. 
