Bulletin - United States National Museum - si-pddr - Smithsonian ...

BIKDS OF ARGENTINA, PARAGUAY, URUGUAY, AND CHILE 85
color. The soft parts in this bird were colored as follows: Maxilla
and base of mandible Eton blue; nail and anterior margin of
maxilla marked with fuscous; mandible, except at base, pale brown-
ish vinaceous; iris Rood's brown; tarsus and toes storm graj^, becoming
dark neutral gray on joints and webs. A male shot on December
3 did not have the sexual organs developed.
On seizing my first specimen of this ruddy duck, I was pleased to
detect in its neck an air sac that, to the sense of touch, appeared
similar to one that I had described in the North American Erisina-
tura janiaicensis.^^
The body of this bird was preserved carefully in alcohol for
subsequent examination. On dissecting it I find the arrangement
on the throat is considerably different from what it is in the North
American bird. In Erismatura vittata the larynx is less highly
specialized than in E. jamaicensis. The fold of connective tissue,
attached to the thyroid cartilage, that I have called the "lifrula
laryngis " is reduced to a slight ridge. The larynx in general has
the cavity anteriorl}'^ compressed from side to side, and posteriorly
expanded. There is no marked division or vestibule in its lower
portion, and the lateral pads found in javiaicensis that I termed
the "pulvini laryngis" are wanting. On the dorsal surface of
the trachea just behind the larynx is a transverse slit that inter-
rupts or divides the upper tracheal ring. The succeeding ring is
broadly notched for half its width, but is not cut entirely through.
This slit forms the opening from the trachea into the tracheal air
sac that extends down between trachea and esophagus.
The neck of this tracheal air sac is long and narrow, while the
elongate sac itself is but little enlarged or swollen. In its total
length from opening to free lower end the sac measures 65 mm.,
while at its greatest distension it is apparently not more than
10 mm. in diameter. It is thin walled and transparent in tex-
ture, ends below at the level of the shoulders, and has no connection,
save through the trachea, with the series of pulmonary
air sacs. The sternotrachealis muscle expands somewhat over the
sac, but is developed merely as a broad, thin fascia of little muscular
strength.
The weak development of the sac, with the small tracheal slit
and lack of specialization of the larynx, are notable when compared
with this structure in Erismatura jamaicensis. The esophagus
of Erismatura vittata., however, is remarkable. The pharyngeal
end has the surface rugose as usual; immediately below the tube
swells in an elliptical expansion that contracts again to normal size
at the level of the shoulder, so that it occupies the same position
^Proe. U. S. Nat. Mus., vol. 52, Feb. 8, 1917, pp. 479-482; Condor, vol., 20,. January,
1918, pp. 19-20.