ON THE ANATOMY OF THE HOATZIN. 467 
the first pair of bronchial semirings with them, to form a box-like 
three-way piece, the pessulus posteriorly running up to join the 
Fig. 2. 
Trachea of Opisthocomus (back view). 
middle of the penultimate ring. The second pair of bronchial semi- 
rings does not articulate with the first, they in all respects seenens 
those nearer the lungs. 
It is possible that what is above considered to be the first pair of 
“bronchial semirings may be the last tracheal ring. That there is a 
small notch interrupting the continuity of the inferior mid-anterior 
margin of the tube formed by the consolidated rings, and that the ring 
above the lowest segment of the consolidated tube is incomplete 
behind, are, however, facts in favour of the former view. 
Among the Galline the only genera which at all approach Opis- 
thocomus, as far as the lower larynx is concerned, are those of the 
Megapodide. 
The two carotid arteries of Opisthocomus, where they meet in the 
front of the neck, become bound together much more intimately than 
in most birds, although at the part where it is impossible to dissect 
away the one vessel from the other, a cross section proves that the two 
tubes are still quite separate. 
Myologically, the great gluteus (tensor fascie of my earlier papers) 
2H 2 
