474 



BIRD. 



considerable deviation from the usual moans of sup- 

 porting the shoulder. The coracoids are strong, 

 they arc well set as far as direction is concerned : 

 but the smallness of the bases by which they are 

 articulated gives them little stability in the vertical 

 plane. They are, however, strongly tied to the 

 shoulders by means of the large blade bones ; and 

 thus the support of the wing, or rather of the swim- 

 ming flap, is thrown as much upon the muscles of 

 the back, and through these as an elastic medium 

 upon the spine, as upon the sternum. 



As these birds use their imperfectly produced 

 wings only in swimming, or in the leaping motion, in 

 which there is no second effort of the wings in the 

 air, and indeed little or no effort of them there at all, 

 the body is never borne up by those appendages, and 

 thus the organisation of greatest ease to the bird is 

 that in which the upper and the under sides contri- 

 bute equally to its support. In its ordinary habit of 

 being in the water, indeed, it is pressed pretty equally 

 by that fluid upon all sides ; and therefore the great- 

 est stability of the clavicle, which is the bone which 

 resists the compressing force in the motion forward, 

 is more stable by having its hold on the back by 

 means of the large scapular. The clavicle is flat- 

 tened, and placed with the edge forward, so that it 

 presents to the water through which the bird moves 

 the greatest stiffness which could be obtained from 

 the same portion of bone ; and its articulation at 

 the shoulder is such that, when there is a strain on 

 the middle part of it, it tends to pull the scapular for- 

 wards. This the broad scapular resists, and it is aided 

 in its resistance by the anterior lateral processes of 

 the sternum, while the equal supports which the flap 

 of wing has from above and from below, enable it to 

 act with equal force in its upward and its downward 

 stroke, and thus perform with more efficiency its fin- 

 like function. The birds of this group are slow and 

 unwieldy, with little capacity of motion either in the 

 air or upon land ; but their organisation is as admirably 

 fitted to their habit as that of any other birds ; and 

 they are curious, as forming the last link between the 

 birds which, as a class, are more typically inhabitants 

 of the air, and those vertebrated animals which are 

 permanently dwellers in the waters, and cannot carry 

 on the process of respiration in the pure air. 



Among the long-legged or long-winged birds which 

 find their food near the waters, in fresh water or in the 

 sea, there is a resemblance in the sternum, but there is 

 also a gradation which may be traced, from the agami, 

 which may be considered as among the least aquatic of 

 the whole, to the cormorants and gannets, and perhaps 

 even to the gulls and terns. This sternal structure 

 docs not of course, in birds of such varied forms and 

 habits, accord with the classification which is usually 

 made of them on the structure of their bills and feet ; 

 but they all agree in being, to a very considerable 

 extent, air-birds ; though none of them, the genus 

 lestris exceptcd, find their food in the air on the wing; 

 and these do not find their own prey in that element, 

 but live upon the food of other birds, which they make 

 these disgorge from their stomachs, and catch it ere it 

 falls. Gulls and terns are the races which are chiefly 

 robbed in this manner, and so prone are they to offer this 

 sort of boon or bribe to real or supposed enemies, that, 

 even in a state of confinement, they will disgorge the 

 contents of their stomachs at the sight of an eagle, or 

 any other formidable rapacious bird. Even the petrels, 

 whose habits are too much seaward for encountering 



predatory or even plundering birds, have this dispo- 

 sition ; for when they are compelled, as they often arc 

 during severe weather, to alight on the decks or 

 rigging of ships, they instantly make a votive offering 

 of the quantity of oil with which their stomachs are 

 loaded. 



The habits of long-legged birds are so diversified 

 they are so much on the land in certain cases, and on 

 the waters or by the sides of them in others that it is 

 not easy to select any species as a fair average of tho 

 whole ; but they follow the general law in having the 

 sternum short in proportion as they are more on the 

 wing, having that bone more elongated, and narrower 

 in proportion, as they are more of walking birds in open 

 places which have not water, and in having the 

 posterior part more divided by notches, in proportion 

 as they are more aquatic. 



Sternum of the agrnni. In their general characters 

 these birds are certainly not a little anomalous ; anc 

 though they are usually classed with the cranes, tc 

 which they have scarcely any other point of resem. 

 blance than a long neck, which after all is net a crane 

 neck, but one fully as like those of the ostrich family 

 they partake of the characters and some of the habits o 

 gallinaceous birds, or rather they partake so equally 

 of the characters of many races, and so little of thost 

 of any one, that in nature they stand alone and dis 

 tinct, whatever may be the place assigned to them ii 

 any system. It is also not a little remarkable, tha 

 the sternum of these birds is as unique as their cha 

 racter ; and this very clearly shows that no classifi 

 cation of birds can be either natural or valuable as ai 

 index to their history, of which the sternal apparatu 

 does not form a considerable and even the leading part 

 This is what we might expect ; because when wi 

 carry our analysis as far as it can rationally be carried 

 that is to the bones which give the entire structure it 

 form and its leading characters, we find that, it is b; 

 tho sternum, and those attached bones the coracoids 

 which are never wanting in a bird, be its habit what i 

 may, and never present in any other animal, that w 

 determine a bird to be a bird and nothing else. Th 

 following figures represent the sternal apparatus of th 

 agami. 



Agami. 



Upon examining these representations, it will b 

 found that the bird to which they have the greato 

 resemblance is the gallinuie ; that the general forn 



