BIRD. 



473 



which does not bear so much on the angle of the 

 keel, and therefore does not press so much upon the 

 sternum, and the viscera which it supports, as in the 

 grebes ; while the sternum, from its greater length, 

 gives more firmness to the under part of the body. 

 The great strain of the shoulder, as the bird moves 

 through the water, is upon the coracoid, chiefly to 

 turn that bone backwards ; and this is resisted by 

 the great enlargement backward at the base, and the 

 embedment of the process of the coracoid and that of 

 the anterior angle of the sternum among the flesh of 

 the shoulder. So that, while the resistance is very 

 powerful, it is at the same time elastic, and not a 

 direct thrust of bone against bone, which would 

 occasion a direct prolongation of the strain through 

 all the bony connexion, instead of an extinguishment 

 of it among the neighbouring parts, as is the case in 

 the mode of articulation here presented. Those 

 direct or jarring strains, propagated all in one direc- 

 tion, are never found in the mechanical structure of 

 animals ; but, on the contrary, the greater the strain 

 upon any one part, the more speedily and widely is 

 it distributed over a number of other parts. 



The form of the clavicle is also a very beautiful 

 part of this structure: the enlargement at the shoulder- 

 joint, the gradual diminution iu^ weight as the bone 

 becomes more curved in approaching the keel, and 

 the way in which the head of the clavicle is united to 

 that of the scapular, so as to bend that bone more 

 firmly against the ribs near the inflexible part of the 

 spine, when the pressure of the water tends to bend 

 the clavicle itself toward the angle of the sternal 

 keel, are all well worthy of close observation : the 

 more so that the natural action of the bird in the 

 water cannot be so easily seen as that of a land bird 

 in the air. Even the point of articulation of the 

 wing is worthy of notice, as having the line of its 

 principal action more in the direction of the general 

 axis of the body than that of wings which are used 

 exclusively in flying. Taken altogether, the divers 

 afford one of the finest and most instructive instances 

 of mechanical perfection which is to be met with in 

 the whole feathered race. Not that their structure 

 is better adapted to their habits than that of any 

 other tribe, for in this all birds, and indeed all animals, 

 may be said to be alike ; but their action is particu- 

 larly energetic ; and the energetic action strikes us 

 with admiration, while in the case of that which is 

 less conspicuous we must examine before we can 

 admire. Those striking cases are of course the ones 

 which it is best to present to those entering upon the 

 study, whether the object be to produce love for the 

 productions of nature, or the inseparable adjunct of 

 that love when grounded aright veneration for 

 nature's Almighty Author. 



3. Sterna of the penguins. In these birds the 

 wings, which in the divers, and also in some of the 

 intermediate genera of auks, are capable of tolera- 

 bly rapid and prolonged flight, so that the birds can 

 not only range over the surfaces of the bays and 

 landward parts of the sea, but migrate from one lati- 

 tude to another as circumstances may require, are 

 incapable of every thing which can with propriety be 

 called flight, though they assist some of the species 

 in a peculiar kind of leaping motion by which they 

 can clear any obstacle with which they meet, by 

 leaping three or four feet clear of the water. English 

 sailors call those which have this habit by the not 

 very inappropriate name of " Jumping Jacks." 



These have the sternum elongated, with the keel 

 well developed, pointed at its angle, and extending 

 considerably in advance of the sternum. The ante- 

 rior edge of the sternum with two large furrows, ter- 

 minating in a depression in some of the species, and 

 in a perforation in others. The sides of the sternum 

 concave in the anterior part, and convex in the 

 posterior. The concave portion having six ribs 

 attached, the last one double ; and the convex con- 

 sisting of a slender process, extending backward to a 

 considerable distance beyond the termination of the 

 middle portion of the sternum, bearing in this respect 

 a very considerable resemblance to that of the galli- 

 nidae. 



The coracoids are long, strong, flattened, having 

 the inner edge formed into a lamina, which is per- 

 forated, and bears at its upper extremity a process of 

 the clavicle. The clavicle has a very peculiar shape, 

 which will be better understood from the following 

 half-size plan of the sternum of the Cape penguin 

 than from any verbal description. 



Cape Penguin. 



The scapulars are very large, much broader than 

 in any other species of bird, and bearing a trace of 

 resemblance to the same bones in the mammalia. 

 Their form will be better seen in the following profile 



Profile of the Cape Penguin 



of the sternal apparatus of the same bird, represented 

 on the same scale. 



It will be perceived that, in those bird:, there is a 



