BIRD. 



461 



The scapular bones are long, bent downwards, pointed 

 at the extremities, but with an enlarged process on 

 the under sides near the middle of their length. The 

 following figure of the sternal apparatus of the jack- 

 daw may be taken as nearly the average of birds of 

 this character. 



Jackdaw. 



None of the birds which have the sternum formed 

 in this manner capture their prey on the wing, or are 

 very rapid fliers, though they are all birds of con- 

 siderable power of flight. They are, however, all, 

 at the same time, birds which are tolerably active on 

 their feet; and the large notches in the sternum, 

 posteriorly towards the sides, enable them to make 

 use of their feet, by the flexure of this part of the 

 sternum, while the average production of the sternal 

 crest or keel admits of tolerably powerful muscles for 

 putting the wings in motion. They are so numerou 

 and so diversified in their habits, that no one type 

 can be properly expressive of them all, but their gene- 

 ral character is that of uniting habits on the wing and 

 on the ground in nearly equal proportions ; and upon 

 comparing their sternal apparatus with those of the 

 birds of powerful wing and the ground birds, it wil 

 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 o 

 the feathers. 



Sterna of the fissirostres. These are all feeders on 

 the wing ; but upon comparing their sternal appa- 

 ratus we find more difference between the diurnal am 

 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. Th 

 sternal crest or keel very much developed, concavi 

 in its front edge, and convex in its under one, wit! 

 the angle where these meet very pointed. Fron 

 edge of the sternum very narrow, with two groove 

 separated by a ridge of bone. The outlines of th< 

 side? concave, generally with five ribs attached tc 

 each, but with six in the white-throated swift (Ci/psc 

 his cottaris). Posterior edge slightly rounded, concav 

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

 notches toward the angles. The following figur 



how the sternal apparatus of the common swift of 

 he 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 

 lot for a powerful but more momentary rush. The 

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

 ect one for the latter purpose, and the difference 

 jetween it and the one now given may in part be 

 bserved by comparing this figure with the sternum 

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



sternum of the golden eagle is also referred to, the 



means of judging will be still more complete and 



satisfactory. 



Swift. 



The sternum of the falcon is firmer and more 

 developed in the anterior part than any of the other 

 two, but it is shorter, narrower at its posterior edge, 

 not so hollow, and weaker from the holes at the 

 angles. That of the eagle is larger backwards, more 

 concave, and the holes are nearly obliterated, but still 

 the anterior part of it is broadest. That of the swift 

 has the posterior part broadest, and the angles have 

 no holes. Thus in the falcon the whole strength of 

 the sternum is concentrated upon that part on which 

 the grand flying muscles are inserted ; and the more 

 perfect arch and uniform strength of the furcal bone 

 harmonise, and render the whole sternal apparatus 

 the most efficient for powerful flight. There is ac- 

 cordingly no bird which has the same desperate rush 

 as the falcon, arid that rush is performed almost ex- 

 clusively by the effort of the wings, and with com- 

 paratively little momentum from gravitation. Indeed 

 a force or momentum produced by gravitation would 

 be a disadvantage to the falcon. She gives chace, 

 and such a momentum would throw her out when 

 her quarry doubles. Thus, though she always attempts 

 to gain and to keep the sky, she never rises to any 

 great height above her prey. 



The more produced sternum, and less perfectly 

 formed furcal bone of the eagle, show that her sternal 

 apparatus is not so exclusively, and therefore not so 

 powerfully, of a flying character. The enlargement 

 of the sternum backwards, and the greater strength 

 of the posterior angles, make it more of a carrying 

 basket, though it retains no small portion of the rapid 

 flight character. But strength rather than swiftness 

 is the character of the eagle's wing. The ordinary 

 flight is floating and hovering, and the wings are 

 more employed in bearing her up than in making 

 progressive motion. When she stoops it is always 

 from a height, and no inconsiderable portion of the 

 force with which she strikes arises from the momen- 

 tum of gravity acquired during the descent. This is 

 further proved by the fact that when the eagle misses 



