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^, be- 

 coming dark neutral gray on joints and webs. A male shot on De- 

 cember 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 con- 

 nection, 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 com- 

 pared 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,. Janu- 

 ary, 1918, pp. 19-20. 



