18 THE FEATUKUED TRIBES. 



being a part of tlie pro\isiou for the attacliincnl of tlio muscles of the wings. The ostrich 

 unci cassowarj', which arc rather ruuncrs than fliers, liave the spine loose. 



" The vcrtebrcB of the back being fixed in birds, and the pslvis reaching high, there is 

 no motion in the body ; indeed, if there -were, it woidd be interrupted by the sternum. 

 We cannot but admire, therefore, the composition of the neck and head, and how the 

 extension of the vertebra), and the length and pliability of the neck, whilst they give to 

 the bill the oificc of a hand, become a substitution for the loss of motion in the body, b}' 

 balancing the whole, as in standing, rminiug, or flying. Is it not curious to observe 

 how the whole skeleton is adajjted to this one object, the power of the wings Y 



" "Whilst the ostrich has no keel in its breast-bone, birds of passage are, on dissection, 

 recognisable by the depth of this ridge of the sternum. The reason is, that the angle 

 formed by this process, and the body of the bone, affords lodgment for the pectoral 

 muscle, the powerful muscle of the wing. In this sketch of the dissection of the swallow, 

 there is a curious resemblance to the human arm ; and we cannot fail to obser\e, that the 

 pectoral muscle constitutes the greater part of the bulk of the body. BorelH makes the 

 pectoral muscles of a bird exceed in weight aU the other muscles taken together, whilst 

 the pectoral- muscles of man ai'e but a seventieth part of the whole mass oi' the muscles. , 

 And here yve sec the correspondence between the strength of this muscle and the rate of 

 flying of the swallow, which is a mile in a minute, for ten hours every day, or 600 miles 

 n day. 3fr. White says truly, that the swift lives on the wing; it eats, drinks, and 

 collects materials for its nest in flymg and never rests but during darkness. If it be true 

 that birds, when migrating, require a wind that blows against them, it implies an 

 extraordinarj' power as v.e[l as continuance of muscular exertion. 



" We see ho^^' nature comjjletes her A\ork, when the intention is that the animal shall 

 rise baoj'aut and jiowerful in the air : the whole texture of the frame is altered and made 

 light, in a manner consistent ^^■ith strength. We .see also how the mechanism of the 

 anterior extremit}' is changed, and the muscles of the triuik difl'erently directed." 



The muscles, as might be supposed, are jjrecisely adapted to the service they have to 

 pcrfonn. The efforts of men to fly in the air are not likely to be more successfid than 

 those of the philosopher described iTi " Rasselas," v.]\o Ibnnd that the </i'.<reiif only was 

 easy, however disappointing and disastrous. Foi- the muscles of the most powerful arm 

 are slender and weak when com})ared with tlie >\ ing-muscles of birds. If, therefore, 

 wings of sufficient ])()wer could be contrived, the ai-nvs would be too feeble to wield them. 

 While it need .scarcely be added that there are no air-cells distributed through tlic human 

 body to diminish its specific gra^■ity by inflation. 



"If each nnisde of flight," says ^I. Cliabriei', ^\ll(l lias paid great attention t<i this sub- 

 ject, " were to contract individually and independently, of tlie rest, it would only put in 

 motion the most moveable parts of the bodj' ^vith which it is especially connected ; there 

 would be no reaction. This asserti(m is true in all i-(>spects ; as, for example, in the depres- 

 sion of the wings dining flight, the resistance or the contraction of tlie middle pectorals and 

 their congeners is absolutely necessary, since, without it, flie ^^•ings would lull by their own 

 weight, and the action of the great jx-ctorals would be useless. IJesides, in the di])ression 

 of the wings, the fixed point of tlu' middle pectoials where tlie n\spective tendons attach 

 themselves to the humerus beiii;^- rcmnved, the sudden contiactidii of these jiectnials must 

 nece.ssarilv facilitate the ascension of the trunk, until th(> hunieiu-; is stopped by the cessa- 

 tion of action in the great pectorals. It may easily lie concc-ived why the jirojecting 

 muscles of the trunk and the depressors of tlie wings are stronger than the elevators; it is 

 because the fonner eause the trunk to start, and by this mi-ans depress tlie wings, not- 

 withstanding the resistance of tlie latter ; these, beint; unable to prevent tlie hiimeius I'mni 

 descending, become fixed there, and draw up the trunk, I luis as.si.sting the action nf the 

 great pectorals, and also jiaiticipating in juojecting llic trunk both forwards and above. 



