be found to partake of the characters of both. The 

 different powers of wing in these birds are in a great 

 measure dependent upon the form and distribution of 

 the feathers. 



STERNA OF THE FISSIKOSTRES. 



The birds which belong to this order are all feeders 

 on the wing ; but upon comparing their sternal appa- 

 ratus we find more difference between the diurnal and 

 nocturnal feeders than in the birds of prey. 



Day -feeders, or the swallow tribe, have the sternum 

 much elongated, often broader toward the rear than 

 the front, and a little hollow on the upper side. The 

 sternal crest or keel very much developed, concave 

 in its front edge, and convex in its under one, with 

 the angle where these meet very pointed. Front 

 edge of the sternum very narrow, with two grooves 

 separated by a ridge of bone. The outlines of the 

 sides concave, generally with five ribs attached to 

 each, but with six in the white-throated swift ( Cypse- 

 lus collaris). Posterior edge slightly rounded, concave 

 on the upper side, and entire, or without any holes or 

 notches toward the angles. The figure on next page 

 shows the sternal apparatus of the common swift of 

 the natural size. 



This may, among birds which naturally resort to 

 Britain, if not among all birds whatever, be considered 

 as the typical sternum for continued flight, though 

 not for a powerful but more momentary rush. The 

 sternum of the jer-falcon is the typical or most per- 

 fect one for the latter purpose, and the difference 

 between it and the one now given may in part be 

 observed by comparing this figure with the sternum 

 i that of the jer-falcon formerly given ; and, if the 

 sternum of the golden eagle is also referred to, the 



