472 STRUCTURE AND CLASSIFICATION OF BIRDS 



ACCIPITRES 



Definition. Aquincubital. Oil gland present. Two carotids. Skull 

 desmognathous and holorhinal. Caeca rudimentary or absent. 

 Ambiens present. Biceps slip absent. 



This large group of birds admits of but a scanty defini- 

 tion, if we are to include in it, as is here done, the secretary 

 bird and the American vultures ; for it then shows a con- 

 siderable amount of structural variation. The oil gland, 



Anc 



FIG. 226. TENSOKES PATAGII OF Polyboroides (AFTER BEDDAED). 

 t.p.l, tensor patagii longus ; t.p.br, tensor brevis ; Anc, ancoujeus ; D, deltoid. 



invariably present, is generally feathered, but nude in the 

 Cathartidse. In Serpentarius this gland varies in size ; in 

 one specimen it was found to be very small and to have a 

 very minute tuft. 



The after shaft is absent in the Cathartidse and in Pandion, 

 present in other Accipitres. Twelve rectrices is the usual 



