•210 DR. PETTIGREW ON THE MECHANISM OF FLIGHT 



extended state are inclined obliquely upwards (PL XIV. figs. 32 & 42), that this ten- 

 rivncy to fallin a downward direction is counteracted. The pectoral muscles, therefore, 

 while they raise and carry the body forwards, also confer upon it the requisite degree 

 of steadiness. The manner in which the weight of a living bird is utilized 



seems 



gut ui di living unu i& utilized is very 



remarkable. 



J n the first place, it gives peculiar efficacy and energy to the down stroke by pressing 

 the inclined planes formed by the wings closely down, upon the wind. 



Secondly, it adds momentum, — a heavy body, when once fairly under weigh, meeting 

 with little resistance from the air, through which it sweeps like a heavy pendulum. 



Thirdly. The mere act of rotating the wings on and off the wind during extension and 

 flexion, with a slight downward stroke, apparently represents the entire exertion on the 

 part of the bird, the rest being performed by weight alone. 



This last circumstance is deserving of attention, the more especially as it 

 constitute the principal difference between a living flying thing and an aerial machine. 

 In the latter, as far as yet devised, there is no sympathy between the weight to be lifted 

 and the lifting power, whilst in natural flight the wing and the weight of the bird act 

 together. If an artificial pinion were properly constructed, it would work up to a great 

 extent the inertia of the machine together with the driving power. In other words, the 

 weight, if made to act upon properly constructed inclined surfaces and suitably directed, 

 would in part be converted into actual lifting power. 



The Bones of the Wing of the Bird— their articular surfaces, movements, SfC- 

 The humerus, or arm-bone of the wing, is supported by three of the trunk-bones, viz. 

 the scapula or shoulderblade, the clavicle or collar-bone, also called the furculum*, and 

 the coracoid bone,— these three converging to form n point (Tappui, or centre of support 



for the head of the humerus, which is received in faeettes or depressions situated 



on the scapula and coracoid. In order that the wing may have an almost unlimited 

 range of motion and be wielded after the manner of a flail, it is articulated to the trunk 

 by a somewhat lax universal joint, which permits vertical, horizontal, and intermediate 



li i t The l0Dg aXiS ° f the ^° int is directed vertically, the joint itself somewhat 

 backwards It is otherwise with the elbow-joint, which is turned forwards, and has its 



directed horizontally, from the fact that the humerus is twisted upon itself to 

 extent of nearly a quarter of a turn. The elbow-joint is decidedly spiral in its nature, 



ements f 



Ion!? 



rLh wT ,"? ^ ° f the Sh0ulde '-J^t at nearly right J^L The humerus 



St! , t W With 2 b ° neS ' the radius «* «» A the IV.nner of which » 

 pushed from the humerus, while the other is drawn towards it during extension, the 



-_ . ,. Y ?. hab " Uall J' ™ M «» gliding and sail™, a, in t lJpZL.i~. *. „ i. «*»» ■ * 



nature. " 



in .ie f ; ; ; r ; , 8 e and ■* abR m in the ****** *• •*- - ° s5s 



... 7_ I'Tf"" 1 ' he furC ° la «• B»™ aaohvlosed with tha JLl L_- /IW An*. 



ofVertebrates. ^ P"f- Owen, vol. ii. p. 66). 



(Comp 



formed 



between the coracoid blJZLl "V ^ tknhted b ? a sma11 funded surface to a corresponding cavity « 

 **. mrA, vol. i. p. 33. SCaHa ' m SUch a mwmCT as *> allow great freedom of motion r^Mac ff il(rvray s 



u mi 



%nt." C>c. o/JnZ t Physiol It hy 4 L m and SOCket - joint ' Pitting all the freedom of motion necessary i* 



