656 CYGNUS IMMUTABILIS. 



The trachea, on reaching the intrafurcular space, forms a 

 slight curve outwards, and then directly enters the thorax. 

 Its width at first is seven-twelfths, then six-twelfths, at the 

 lower part of the neck nine-twelfths. It is composed of a 

 hundred and ninety rings, and five united rings forming the 

 inferior laryngeal bone, which is moderately compressed, its 

 breadth being six-twelfths, and its posterior margin, which 

 is very oblique, almost an inch in height. It differs from 

 that of the other species in having the terminal margin thus 

 oblique, and in wanting the external, lateral, narrow, free 

 membranes, there being in this species none besides those 

 intervening between the last tracheal and first bronchial 

 rings, about the middle of which, however, is seen the very 

 slender bone appended to the narrow membrane in the others. 

 The bronchi are very short, only an inch and a half in length, 

 Avith fifteen incomplete, slender, and feeble rings. 



The skin at the base of the bill, including the frontal 

 knob, and the large triangular space from the lateral base of 

 the upper mandible to the eye, and surrounding it, is bare. 

 The nostrils are oblong, patulous, seven-twelfths in length, 

 in the lower anterior part of the oblong nasal sinus. The 

 eyes are very small, their aperture measuring five-twelfths 

 and a half. The legs are very short and strong ; the tibia 

 bare for an inch and a quarter ; the tarsus compressed and 

 reticulate. The first toe very small, with an inferior slight, 

 compressed lobe, reticulated above, but having also four scu- 

 tella ; the second toe with eighteen, the third twenty -five, the 

 fourth thirty-one scutella ; the inner with a broad margin or 

 web ; the interdigital membranes full. The claws stout, 

 moderately arcuate, rather obtuse, that of the middle toe 

 dilated and rounded. 



The plumage rather full, dense, soft, and elastic ; on the 

 head and neck the feathers oblong, obtuse, blended ; on the 

 other parts ovato-oblong. The wings are very long, of mode- 

 rate breadth, convex ; the quills thirty-five ; the primaries 

 strong, decurved, the outer three strongly simiate on the 

 inner web, the second and third longest and about equal. The 

 tail is short, rounded, of twenty-four feathers. 



The bill is orange-red, with the margins of the upper 



