BIRD. 



477 



part of it is divided among the coracoids, the scapu- 

 lars, and the keel of the sternum, though the greater 

 part, of it goes in the direction of the first of these. 

 They are well adapted, both from their form and the 

 mode of their attachment to the sternum, for resisting 

 the strain of a pressure from the front. The basal 

 parts arc very large, and so are the heads, with which 

 the branches of the clavicle are in all cases firmly 

 united, and in some they are soldered into one 

 continuous bone. 



Profile ot Cormorant. 



And there is no waste of strength in the firmness 

 against a pressure from the front which is thus given 

 to the shoulders of these birds ; nor is the advance- 

 ment of the clavicle in front of the shonlder-joint, or 

 the strength which it receives there from its increased 

 curvature and breadth, and its intimate union with 

 the head of the coracoid, without an object and use 

 in the economy of the bird. 



These birds do not make way with their whole 

 body in the water, as is the habit of the divers ; but 

 they take the water with much more force, and there- 

 fore with a greater shock upon their bodies. Almost 

 all of them plunge headlong on their prey in the 

 water, and some of them do so from a great height 

 a height from which if even the strongest of the 

 mammalia were to fall on their feet upon the water 

 they would be in danger of dislocating their joints, o 

 even breaking their bones. All who are in any way 

 familiar with the water must be aware how dangerous 

 it is to descend into that liquid, even from an incon 

 siderable height, in any other way than head foremost 

 and especially how very hazardous it is to jump int 

 it from a greater height with the legs apart from 

 each other. Many of the birds of this tribe descen 

 from heights and with velocities which, notwithstand 

 ing their feathery covering and the yielding nature o 

 the fluid on which they descend, would, if its etfec 

 came as a cross strain, break the stoutest bone in 

 their bodies. The bird from its form penetrates th 

 water easily, and the articulations of the neck are s< 

 many, and so free in their motions, that any shoe" 

 which the head may receive by the plunge is s 

 divided among them as not to occasion the least con 

 cussion of the contents of the skull. Thus the part 

 which come into the severest contact with the wate 

 are the shoulders : and this is met by the strong an 

 comparatively narrow parts of the arches in the direc 

 tion of the vertical plane. And, upon examining th 

 front view of the sternum, it will be found that, beside 

 the hold which the scapulars have on the back an 

 the stiffness given by the clavicle, the great breadt 

 of the coracoids at their bases, and the form of th 



nes of their union with the sternum, afford a very 

 rtn base in the cross direction. 



The more typical of these birds are not very rapid 

 iers, but many of them are much on the wing ; and 

 icy fly by powerful strokes rather than quickly- 

 epeated ones. Hence they have the sternum broad, 

 nd the fibres of the pectoral muscles long, so that, ' 

 n the principle formerly explained while noticing 

 :ie wings of the anisodactyli, these wings sweep over 

 arge arches and with much power, though slowly as 

 ompared with birds that have the sternum narrower 

 and the muscular fibres shorter. 



There is another advantage which this large sweep 

 nit slow motion of the wing has over a shorter and 

 [uickcr one : the wind has much less effect either in 

 atiguing the bird or in drifting it to leeward ; and 

 icnce we find that most sea birds have this long and 

 swinging flight, whether they belong to this family or 

 not. Those of this family are of course not the best 

 liers among sea birds, as their sternal apparatus is 

 not formed wholly for flight, but for that and resisting 

 the plunge jointly ; aud as each of these requires a 

 different structure, each of them must, to some ex- 

 tent at least, weaken the other. 



Sterna of the Longipenncs. These have some re- 

 semblance to those of the former tribe, and also to 

 those of the grallida?, as might be expected from the 

 jirds partaking in part of the habits of both ; but 

 they have also habits which are more peculiarly their 

 own, and the sternal apparatus is modified to accord 

 with these. Not only this, but as there is a gradation 

 from the gulls, which feed on the wing, and also, in 

 walking on the shore, to the petrels, which are more 

 exclusively seaward, and walk little : but there are 

 so many modifications of the sternal apparatus, that 

 no single bird can be selected as an average type of 

 the whole. We shall therefore select two speci- 

 mens : the. laughing gull as nearly an average of the 

 more landward subdivision, and the puffin petrel as 

 nearly an average of the more seaward. 



The sterna of the skuas, gulls, and terns, are in 

 their general form intermediate between those of the 

 entire footed birds and of the waders. They are 

 rather longer and not quite so broad in proportion as 

 those of the former ; but broader and less elongated 

 than those of the latter. The keel also, though well 

 developed, is not so high in proportion to the width 

 of the sternum. From this structure it follows that 

 the motion of their wings, though more powerful, 

 must be slower than that of the waders ; and the 

 wing itself is longer in its bones and its feathers, as 

 well as in those muscles which put it in motion. 

 This structure accords with the general habit, which 

 is that of skimming about with smooth and mode- 

 rately swift wing, and culling their food from the 

 crests of the waves, or from substances cast up by the 

 waters and left upon the strand. The keel of the 

 sternum is deeply concave in front, with the angle 

 much rounded ; and the posterior part, which is 

 nearly square at the end, is divided more or less 

 deeply by four notches, the two middle ones of which 

 are larger in some of the species, and the two lateral 

 in some of the others. The posterior, or carrying 

 part, of the sternum is rather broader than the middle 

 part to which the ribs, which are six or seven, are 

 attached ; and the lateral processes extend on the 

 flanks without any bending inwards. The coracoids 

 are strong and well set, the clavicle wide, convex 

 anteriorly on the upper parts of its branches, but 



