HOACTZIN 423 
at which Garrod subsequently arrived after closely examining and 
dissecting specimens preserved in spirit; but the latter has gone 
further and endeavoured to trace more particularly the descent of 
this peculiar form and some others, remarking that the ancestor of 
Opisthocomus must have left the parent stem very shortly before the 
true Galline first appeared, and at about the same time as the inde- 
pendent pedigree of the Cuculidex and Musophagide commenced— 
these two groups being, he believed, very closely related, and 
Opisthocomus serving to fill the gap between them. Still more 
recently Dr. Gadow has shewn that the very singular modification 
of the sternal structure in this form is chiefly due to the extra- 
vagant enlargement of its crop. 
It would be impossible here to state at length the facts on 
which these views are grounded, and equally impossible to give 
more than a very few details of the anatomy of this singular form. 
The first thing that strikes the spectator of its skeleton is the 
extraordinary structure of the sternal apparatus, which is wholly 
unlike that of any other bird known. The keel is only developed 
on the posterior part of the sternum—the fore part being aborted, 
or, as it were, cut away, while the short furcula at its symphysis 
meets the manubrium, with which it is firmly consolidated by means 
of a prolonged and straight hypocleidium, and anteriorly ossifies 
with the coracoids. This unique arrangement seems to be corre- 
lated with the enormously capacious crop, which rests upon the 
furcula and fore part of the sternum, and is also received in a cavity 
formed on the surface of each of the great pectoral muscles. Further- 
more this crop is extremely muscular, so as more to resemble a 
gizzard, and consists of two portions divided by a partial constric- 
tion, after a fashion of which no other example is known among 
birds. 
The Hoactzin appears to be about the size of a small Pheasant, 
but is really a much smaller bird. The beak is strong, curiously 
denticulated along the margin of the maxilla near the base, and is 
beset by diverging bristles. The eyes, placed in the middle of a 
patch of bare skin, are furnished with bristly lashes, resembling 
those of Hornbills and some few other birds. The head bears a 
long pendent crest of loose yellowish feathers. The body is olive- 
coloured, varied with white above, and beneath is of a dull bay. 
The wings are short and rounded. The tail is long, and tipped 
with yellow. The legs are long, the feet stout, the tarsi reticulated, 
and the toes scutellated; the claws long and slightly curved. 
According to all who have observed the habits of this bird, it lives 
in bands on the lower trees and bushes bordering the streams and 
lagoons, seldom taking wing, and then flying weakly, feeding on 
leaves and various wild fruits, especially, says the late Mr. Bates 
(Nat. Amaz. i. p. 120), on those of a species of Psidium, and it is 
