466 ON THE ANATOMY OF THE HOATZIN. 
so decisive of its affinities as in many cases, the reason being that so 
great an amount of the unfeathered spaces is protected by semi- 
Trachea of Opisthocomus (front view). 
plumes. May not these semiplumes in many instances be degene- 
rated feathers? 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 
Page 112. facts to add. I may, however, mention that it is only in the Cracide, 
among allied birds, that the vomer runs so far forward in the palate at 
the same time that it is tumefied at its anterior extremity. In Ortalis 
albiventris this is most strikingly the case. 
The alimentary canal has been so fully described by L’Herminier,* 
that it is quite unnecessary for me to enter into detail with reference 
to it. . . 
Johannes Miillert has noted one or two points concerning the wind- 
pipe. Figs. 1 and 2 represent its anterior and posterior aspects. 
The lowermost four tracheal rings are consolidated together, and 
* “ Comptes Rendus de |’ Acad. des Sciences,” 1837, vol. v. p. 435. 
+ “ Berichte Akad. d. Wissenschaft. z. Berlin,’ 1841, p. 177. 
