ORDER CHENOMORPFLE 



Subordeb Anseres (Ducks, Geese, and Swans) 

 Family Anatid^e 



Ducks are typically shorter-necked than geese and swans, with fewer neck ver- 

 tebrae. In common with other members of the suborder, they are adapted for a more 

 or less aquatic life, with webbed feet for swimming (except in Anseranas) and a broad 

 more or less flattened bill provided with horny lamellae about the edge, for sifting 

 out food from muddy water. They agree in having a tufted oil-gland (presumably a 

 derived rather than a primitive character); the feathers are provided with a small 

 after-shaft, which, however, is sometimes absent. In the arrangement of the feathers, 

 the dorsal tract divides about halfway down the neck, enclosing a long narrow me- 

 dian space, and the pectoral tract likewise divides at about the same level, giving off 

 an outer band on each side. The wing has the diastataxic interval. 



The muscular anatomy is remarkably uniform throughout the group. One pecu- 

 liar duck character, but found also in the loon, tinamus, and some fowls, is the meet- 

 ing of the two great breast muscles over the keel of the sternum. Another marked 

 peculiarity of the group is that the biceps femoris muscle gives off a tendinous slip 

 attaching it to the gastrocnemius muscle, a condition found elsewhere, curiously, in 

 the ostrich. In all members of the group, the muscle formula of the hind leg is ABX+, 

 which means that of the five muscles important in classification, the femoro-caudal 

 and its accessory head are present, as well as the ambiens, while the semitendinosus, 

 though present, lacks the accessory portion that is often found arising from the distal 

 end of the femur. Characteristic of the group and of the related screamers (Pala- 

 medeidae) is the possession of two pairs of extrinsic tracheal muscles (i.e., muscles 

 having one attachment only to the trachea) and one pair of intrinsic muscles (both 

 origin and insertion on the trachea) attached in ducks to the third or fourth tracheal 

 ring in front of the syrinx. In most ducks, at least in the males, the trachea at its 

 junction with the two bronchi becomes dilated to form an asymmetrical bulbus or 

 chamber of varying size. In the geese this enlargement is not found, but its place is 

 taken by a bony tube formed by fusion of the tracheal rings. 



In the possession of from sixteen to nineteen vertebrae in front of those bearing 

 ribs, the ducks and geese differ from the swans in which there are from twenty -three 

 to twenty-five. In most ducks the number is sixteen or seventeen; in geese, nineteen. 

 The following osteological characters of the Anseres are drawn up by Seebohm 

 (1889): (1) the dorsal vertebrae are heteroccelous (i.e., the articulating surface is 



