730 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 



=Heterodactijlx Sclater, Ibis, Oct., 1880, 401, in text. — Dubois, Mem. Soc. 

 Zool. France, 1891, 115. 



= TrogoniniV A. Milne-Edwards, Ois. Foss., ii, 1867-1871. 



= Trogonoideae Stejneger, Stand. Nat. Hist., iv, 1885, 433, in text. 



= Trogonoidei Cope, Am. Nat., xxiii, Oct., 1889, 872, 873. 



= Trogones American Ornithologists' Union, Check List, 1886, 208. — Fuer- 

 BRiNGER, Unters. Morph. Syst. Vog., 1888, 1567. — Seebohm, Classif. Birds, 

 1890, pp. vii, xi, 8.— Sharpe, Rev. Classif. Birds, 1891, 92; Hand-list, ii, 

 1900, 146.— Gadow, in Bronn's Thier-Reich., Vog., ii, 1893, 254, 301; Classif. 

 Vertebr., 1898, pp. xv, 37.— Beddard, Struct, and Classif. Birds, 1898, 

 202.— Knowlton, Birds of the World, 1909, 50. 



Zygodactyloiis but heterodactyloiis 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; me taste rnum 4-notched; spina interna ab- 

 sent, spina externa present (long and bifid) ; coracoids touching but 

 not connected ; hypotarsus complex; cervical vertebrae 15; complete 

 ribs, 4-5 pairs; syrinx tracheo-bronchial ; only the left carotid artery 

 developed; caeca 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 quin to- 

 cubital; young gymnopsedic. 



The Heterodactylse are a strongly characterized group of Coracii- 

 form birds which combine the cranial characters of the Ca])rimulgi, 

 the myological formula of the Alcedinidas ( = Anisodactylse, part), and 

 an oscinine pterylosis with an entirely unique arrangement of the toes 

 and the deep j)lantar 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 wdtli those of the other z3^godactyle 

 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. 



