ON THE ANATOMY OF THE HOATZIN. 465 
78. NOTES ON POINTS IN THE ANATOMY OF THE 
HOATZIN (OPISTHOCOMUS CRISTATUS).* 
Proressor Newron having most kindly placed in my hands for dissec- Page 109. 
tion three specimens of Opisthocomus cristatus preserved in spirit, I am 
able to add a few details to the accounts which have already appeared 
on the structure of this peculiar bird. 
In his valuable paper in this Society’s ‘ Proceedings,t}’ “ On the 
Classification and Distribution of the Alectoromorphe and Hetero- 
morph,” Professor Huxley describes in detail the skeleton of Page 110. 
Opisthocomus, concluding, as the result of his study of the bird, 
that it should constitute a group (the Heteromorphe) by itself, 
which sprang direct from the main stem of Carinate descent, later 
than the Tinamomorphe, Turnicomorphe, and Charadriomorphe, 
but before the Gallinaceous birds, Sand-Grouse, and Pigeons were 
developed. 
Since then, in our “ Transactions,”{ Mr. J. B. Perrin has published 
a myological account of the species, in which he, however, compares 
it with few other birds. One of Mr. Perrin’s figures§ very excel- 
lently represents the form and situation of the immense crop, as well 
_ as the situation, in the unfleshed bird, of the expanded margin of the 
short carina sterni, from which an accidental error made by Nitzsch, 
who evidently had an imperfect skin to work upon, may be corrected. 
Nitzsch, in his “ Pterylography,” figures (and the drawing is repro- Page 111. 
duced in Mr. Perrin’s memoir), the outline of the furcula and sternum, 
and does it as if the bird were not peculiar in the pectoral region. But 
as the crop occupies almost all the upper part of the breast, and by its 
magnitude distorts the furcula and sternum, the outline is quite incor- 
rect. What is more, there is in the bird itself an oval area, about 
‘75 inch long from above downwards, and °25 inch in breadth, of 
dense naked skin, covering the surface of the expanded upper cutane- 
ous surface of thecarinasterni. This is omitted in the drawing. The 
area surrounding this is unfeathered, although I find well-developed 
plumes in the middle line above it, and no trace of any longitudinal 
median space of any kind over the surface of the crop or neck. 
Opisthocomus is one of those birds in which the pterylosis is not 
* “Proceedings of the Zoological Society,” 1879, pp. 109-14. Read, Febr. 4, 
1879. 
+ “Proceedings of the Zoological Society,’’ 1868, p. 294. 
| t “ Transactions of the Zoological Society,” vol. IX. p. 353. 
: § Loe. cit. pl. lxiii. fig. 3. 
2H 
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