422 HOACTZIN 
the Linnean genus Phasianus, some of its many peculiarities were 
recognized by Illiger in 1811 as sufficient to establish it as a dis-. 
tinct genus, Opisthocomus ; but various positions were assigned to it 
by subsequent systematists, whose views, not being based on any 
information respecting its internal structure, do not here require 
particular attention. L’Herminier, in 1837, was the first to give 
any account of its anatomy (Comptes Rendus, v. p. 433), and from 
his time our knowledge of it has been successively increased by 
many authors.! 
After a minute description of the skeleton of Opisthocomus, with 
the especial object of determining its affinities, Prof. Huxley (loc. 
Hoactzin. 
cit.) declared that it ‘resembles the ordinary Gallinaceous birds and 
Pigeons more than it does any others, and that when it diverges 
from them it is either sw generis or approaches the Musophagide.” 
He accordingly regarded it as the type and sole member of a group, 
named by him HETEROMORPHA, which sprang from the great 
Carinate stem later than the Zinamomorphe, Turnicomorphe, or 
Charadriomorphx, but before the Peristeromorphex, Pteroclomorphx, or 
Alectoromorphx. This conclusion is substantially the same as that 
1 Johannes Miiller, Ber. Akad. Wissensch. Berlin, 1841, p. 177; Deville, 
Rev. Zool. 1852, p. 217; Gervais, Hxpéd. Amérique du Sud, Zool. Anat. 
(Castelnau), p. 66; Huxley, Proc. Zool. Soc. 1868, p. 804 ; Garrod, op. cit. 1879, 
p- 109; Perrin, Trans. Zool. Soc. ix. p. 583; Parker, op. cit. xiii. pp. 43-85 ; 
C. G. Young, Notes Leyd. Mus. x. pp. 169-174, pl. 8; Quelch, Zbis, 1890, pp. 
327-335 ; Gadow, Trans. R. Irish Acad. ser, 3, ii. pp. 147-154, pls. vil, viii. 
