460 



BIRD. 



even with the anterior part of the bone, and sometimes 

 in advance of it, with the edge thickened, as if it con- 

 sisted of two pieces united together ; the keel much 

 higher at the place where the great pectoral muscle 

 is inserted than at the insertion of the middle one. 

 The sides are a little concave, and the ribs vary from 

 five to seven ; the posterior edge generally nearly 

 straight, with a lateral hole in each angle, but these 

 are often nearly, and sometimes wholly, obliterated 

 by bone. There is not, even in the youngest stage 

 of the more typical birds, any appearance of distinct 

 bones forming the sternum, as there are iu birds of 

 some other orders, but the process of ossification 

 begins at the fore-part, and proceeds regularly back- 

 wards. 



The coracoids are shorter than the sternum, but 

 very strongly formed, and their internal angles, where 

 they are attached to the sternum, often meet each 

 other. The clavicles form a complete arch, more or 

 less depressed toward the centre, having its depth 

 placed in the direction of the strain ; of nearly equal 

 strength throughout its length in the falcons, which 

 are the birds of most rapid and continuous flight, but 

 diminished toward the middle in most of the others ; 

 and firmly united at both extremities to the scapulars 

 and the coracoids. 



The scapulars are a little longer than the sides of 

 the sternum, oval in their section, slightly curved, 

 pointed at their extremities, and firmly united with 

 the coracoids and clavicle at the angle of the shoulder, 

 a little above the articulation of the humerus, to which 

 they afford a very firm point of support, and to the 

 tendon of whose elevating muscle they furnish a very 

 perfect pulley. 



Golden Eagle. 



We have given in the above cut a profile of the 

 sternum of the golden eagle, as about the average of 

 the order, and we add the humerus, to show the 

 relative size of that bone, as well as the enlarged pro- 

 cesses on both ends, which serve as levers upon which 

 the tendons act in a very powerful wing. 



From what has been already said, the different 



parts of this as well as of the other sterna which are 

 to follow, will it is hoped be understood without the 

 somewhat clumsy expedient of letters of/eference. 



This is the average type of the sternal apparatus 

 of the diurnal birds of prey, to which some are supe- 

 rior and some inferior. The most perfectly formed 

 are the noble hawks or falcons, of which some notion 

 may be formed by looking back at the sketch of the 

 most perfect of the whole, the jer-falcon, at page 405. 

 The short-winged hawks, buzzards, harriers, kites, 

 and eagles follow ; and after them the fishing eagles, 

 the vultures, and the skuas, which last, though they 

 do not kill game, yet rus>h upon the gulls and other 

 birds, which they plunder, with strong and rapid w ing. 

 They have, no doubt, their sternal apparatus some- 

 what modified so as to accord with their webbed feet 

 when they do take to the water, but still they are 

 chiefly and characteristically air-birds. 



The secretary falcon, which combines with some of 

 the characters of the diurnal birds of prey some of 

 those of the grallidae, which frequent not the waters 

 or their margins, has the keel of the sternum less 

 perfect, the posterior edge terminating in a point, and 

 the general outline curved something in the same 

 manner as that of the wingless birds. The clavicle 

 has also an enlarged process at the junction of the 

 two branches, which rests upon the sternum ; and the 

 coracoid bones are proportionally much longer than 

 in the typical birds of prey. There is, in short, 

 enough in the structure of this bird (and the habit 

 corresponds) to show that it ought not to be classed 

 with the accipitres ; but not enough to bring it pro- 

 perly into any other order or family. 



In the nocturnal birds of prey there are also con- 

 siderable differences in the formation of the sternal 

 apparatus. The snowy and eagle owls, which are 

 more bold and daring than the rest, have the furcal 

 bone formed more into an arch, and the keel of the 

 sternum better developed than in the common owls, 

 which are birds of weak flight, feeding on reptiles 

 and small mammalia, and chiefly in the twilight. But 

 the whole of this division have the skeleton so much 

 more feeble iu all its parts than the diurnal preyers 

 that, in a strictly natural system, they ought perhaps 

 to be wholly separated. The common owls have the 

 posterior edge of the sternum with notches, generally 

 two on each side, filled by membranous or cartila- 

 ginous matter, and they have the arms of the clavicle 

 or furcal bone straighter, and with its flat side placed 

 more in the direction of the strain than in the diurnal 

 birds of prey. This accords with the comparative 

 slowness of their flight, and the feeble and downy 

 character of their flying feathers. 



Sterna of the omnivorous birds. The character of 

 the sternum is much the same in the greater part of 

 those birds which form the extensive and otherwise 

 diversified order of passeres. They have the sternum 

 longer than broad, enlarged toward the posterior ex- 

 tremity, and with two deep notches toward the sides. 

 The keel is moderately produced, convex on its under 

 side, and concave to the front, which has a forked 

 process upon which the middle of the furcal bone 

 rests. The coracoid bones are longer than the 

 sternum, slightly bent, or coulter-shaped, with an 

 enlargement near the shoulder-joints, and narrowed 

 toward the* extremities. The clavicle is long and 

 bent downwards at the middle, generally rather nar- 

 row, and united to the forked process of the sternum. 



