1879.] 



ANATOMY OF THE HOATZIN. 



Ill 



drawing is reproduced 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 incorrect. 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 cutaneous surface of the carina sterni. This 

 is omitted in the drawing. The area surrounding this is unfeathered, 

 although I find well-developed plumes in the middle line above it, 



Fi- 2. 



Trachea of OpistJwcomus (back view). 



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 

 so decisive of its affinities as in many cases, the reason beinc that so 

 great an amount of the unfeathered spaces is protected by semi- 

 plumes. May not these semiplumes in many instances be de- 

 generated feathers 1 This question has never been decided, so far as 

 I am aware. 



To our knowledge of the osteology of the Hoatzin I have no fresh 



