479 BIRD 



recurved at their junction, and always united to the 

 keel of the sternum. The scapulars are scithe- 

 shaped, rather long, and of moderate breadth. From 

 its structure, this sternal apparatus indicates consider- 

 able power of flight, and also strength for resisting 

 pressure on the anterior part, though in this last 

 respect it is much inferior to that of the entire footed 

 birds ; and in both it is very interior to that of the 

 petrels. The following figures of the sternum of the 

 laughing gull, and more especially the lower one which 

 represents the profile, will illustrate this structure. 



Laughing Gull. 



The sternal apparatus of the petrels is much better 

 formed both for flight and for resistance of pressure 

 against the front. It is short and broad, rather nar- 

 rower in the middle than towards the extremities, 

 very concave on the upper surface, and consequently 

 convex on the under. The keel much produced, 

 extending with some elevation to the posterior ex- 

 tremity of the sternum, but much more elevated in 

 front, convex in its under outline, and concave in the 

 front one ; the angle much produced, rounded, and 

 supporting the clavicle, which is enlarged at the 

 junction of its branches. The latcraj processes oi 

 the sternum are well produced, the grooves deep, and 

 the coracoids firmly attached by large bases. The 

 sides concave upwards, carrying six ribs. The poste- 

 rior edges differing 1 in different genera, being entire 

 in the storm-petrels, having a large notch on each 

 side in the albatross, and two small ones on each side 

 in most of the others. The coracoids are strong in 

 their whole length, but remarkable for the extent oi 

 their bases and the largeness of their heads, from the 

 first of which structures they form a perfect arch in 

 the lateral directions, even without the assistance ol 

 the clavicle. But the clavicle is also strong, and 

 capable from its curvature of offering a powerful re- 

 sistance to any strain, whether lateral or from the 

 front. The scapular is slender, very slightly curved 

 downwards, and continued in the same curve with 

 the upper part of the clavicle. This is indeed one 

 of the firmest shoulders which occurs in the whole 



class ; and, as will be seen from the profile in the 

 following figure, the keel of the sternum, the coracoid, 

 and the scapular form a very perfect ellipse, extend- 

 ing to about three-fourths of an entire circumference. 



Puffin Petrel, half the size of nature. 



Though the sternal apparatus of all these birds 

 possesses great power, that power does not indicate 

 an equal capacity of flight in the whole. The differ- 

 ences as connected with flying are chiefly found in 

 the posterior edge ; and as we have them in birds 

 which have the rest of their sternal apparatus very 

 much alike, and have the habit of flying connected 

 with each, we are thereby better enabled to judge of 

 the difference between entire and partially divided 

 sternums than if we had the means of comparing 

 these only in birds which less resembled each other 

 in other respects. The different species of storm 

 petrels which have the sternum entire, and conse- 

 quently the firmest origin for their pectoral muscles, 

 are among the most continued and excursive fliers 

 of which we have any knowledge. The wide sea is 

 their pasture, and, be its extent what it may, they 

 range from shore to shore ; now rushing at a mode- 

 rate height through the air, with light wing and with 

 great velocity ; again skimming close to the surface, 

 so that the points of their wings tip the water at every 

 stroke ; and yet again running along the water, with 

 'expanded wings, which, though they seldom move, 

 float them so buoyantly that they just touch the 

 water with the points of their webs, and thus paddle 

 swiftly along, collecting on the feathers of their 

 breasts that floating pellicle of oil which forms no 

 inconsiderable portion of their food, and which, when 

 they have wearied themselves in skimming, they lean 

 on the wave, and remove with the bill at their leisure. 



The albatross, which, though a very long-winged 

 bird, has a more heavy and gull-like flight than the 

 storm petrels, has, as already noticed, one notch in 

 each posterior angle of the sternum, by means of 

 which those parts of the bone are rendered feebler. 

 These birds are scavengers for larger matters rather 

 than skimmers of the oil of the sea, like the preceding 

 genus, but they are wide ranging scavengers, and, 

 when they are once on the wing, miles of ocean are 

 of little consequence to them in their range. 



The common petrels, and other birds which have 

 four notches in the posterior part of the sternum, are 

 inferior to the others both in the style and the rapidity 

 of their flight, and a connexion may be traced perhaps 

 as naturally from them through the puffins and auks to 

 the wingless birds, as that which is traceable from the 

 divers. The whole of this family may, however, be 

 considered as the most pelagic of all bird?, because, 



