SUBFAMILY DENDROCYGNINM 



The Tree Ducks include several very distinct species all, however, referable to the 

 single genus Dendrocygna and constituting a well-defined group. They exhibit cer- 

 tain very gooselike characters that have induced some authors to associate them 

 with the Anserince but the weight of evidence favors placing them among the ducks. 

 Some have included them among the Anatince, or typical ducks, but their peculiar 

 combination of characters seems sufficient to accord them the rank of a separate 

 subfamily. As in the true ducks, the number of vertebrae in front of the pygostyle is 

 never more than forty-four, whereas in the typical geese there are never less than 

 forty-seven. Of external characters peculiar to the subfamily the more diagnostic 

 are the long legs with the reticulated instead of scutellated skin of the lower tarsus. 

 In addition, the skull is extraordinary in that the tip of the lachrymal bone, which 

 is free in other Anseres, is here produced backward so as to unite with the squamosal 

 process, thus completely enclosing the orbit in a bony ring. The pelvis is unusually 

 shortened and bent down posteriorly, and the pubic bones are slender at their tips as 

 in other ducks. The trachea of the males has a symmetrical enlargement at its 

 base, corresponding to the asymmetrical osseous bulla in males of the more typical 

 ducks. 



