Page 525. 
376 ON THE ANATOMY OF PASSERINE BIRDS, 
tracheal is incomplete in the middle line in front, as well as at the 
sides, whilst behind it is thickened, and sends small downward 
processes on each side of the middle line in such a manner as to 
develop a notch between them. Figure 3 represents the left-side 
view of these structures, seen from the interior of the organ, a being 
the processus vocalis. From figure 1 it can be seen that the tracheal 
rings four, five, and six from the bottom are not ossified at all in front, 
and that rings seven, eight, and nine are only so at their sides, whilst 
ring ten, with those just above it, are extremely thin in the middle. 
Posteriorly also, from figure 2 it can be inferred that the rings above 
the bottom ones are very slender, becoming thicker by degrees above 
the sixth, which is the highest of those constituting the voice-organ. 
With reference to the muscles, it may be stated that the lateral 
muscle of the trachea on each side covers and joins the upper ex- 
tremity of the processus vocalis, turning off to become the musculus 
sterno-trachealis opposite the ring third from the end, and sending no 
continuation on to act directly upon the bronchial semi-rings. 
Iipaugus cineraceus.—In this species the single specimen at my 
disposal, which Mr. Edward Bartlett has most kindly given me, has 
the lower part of the windpipe considerably damaged by shot. Never- 
theless, as one side is comparatively uninjured, I have been able to 
make out the essential points in the structure of the syrinx, which 
does not differ much from that of Pipra leucocilla, as represented by 
Miiller.* The lowermost rings of the trachea are not peculiar, each 
one being deep, and meeting, at its superior and inferior margins, 
the rings above and below it. The first and second bronchial semi- 
rings resemble those of the trachea in their flatness, depth, and 
approximation, the third being the first normal bronchial ring. It, 
with those which follow, are slightly peculiar in that they are ossified 
throughout, except in a small part, equal to about one sixth the 
breadth of each semi-ring, one third distant from their anterior ends, 
where they retain their primitive cartilaginous structure (vide Plate 
[27] LIII. figs. 6 and 7). 
The lateral muscle of the trachea is of considerable breadth, being 
most developed anteriorly, those of the opposite sides coming nearly 
into’ contact in the middle line in front. Opposite the tracheal ring 
seventh from the bottom, the small sterno-trachealis is differentiated 
off from the posterior portion of this muscle, by far its larger anterior 
part continuing downwards to become the intrinsic muscle of the 
syrinx, which ceases at its insertion into the anterior half of the third 
bronchial semi-ring. It exhibits no tendency to split into two as in 
Pipra leucocilla. 
* Loc cit. Plate IV. figs. 9-11. 
