DR PETTIGPEW ON THE PHYSIOLOGY OF WINGS. 395 



the bat and bird, as this has been satisfactorily done already. I will, therefore, 

 confine the present remarks to the elastic ligaments, and more especially to those 

 of the bird, as being the most illustrative, alike from their size and situation. 



The Wing Flexed and partly Elevated by the Action of Elastic Ligaments — 

 the Nature and Position of such Ligaments in the Pheasant, Snipe, Crested Crane, 

 Swan, &,c. — When the wing is drawn away from the body of the bird by the 

 hand the posterior margin of the pinion formed by the primary, secondary, 

 and tertiary feathers rolls down to make a variety of inclined surfaces with the 

 horizon. When, however, the hand is withdrawn, even in the dead bird, the wing 

 instantly folds up ; and in doing so, reduces the amount of inclination in the several 

 surfaces referred to. This it does in virtue of certain elastic ligaments, which are 

 put upon the stretch in extension, and which recover their original form and posi- 

 tion in flexion. This simple experiment shows that the various inclined surfaces 

 requisite for flight are produced by the mere act of extension and flexion in 

 the dead bird. It is not, however, to be inferred from this circumstance that 

 flight in the animal kingdom is a purely mechanical act any more than ordi- 

 nary walking is. The muscles, bones, ligaments, feathers, &c. are so adjusted 

 with reference to each other that if the wing is moved at all, it must be moved 

 in the proper direction — an arrangement which enables the bird to fly without 

 thinking just as we can walk without thinking. There cannot, however, be a 

 shadow of a doubt that the bird has the power of controlling its wings both 

 during the down and up strokes; for how otherwise could it steer and direct 

 its course with such precision in obtaining its food 1 how fix its wings on a level 

 with or above its body for skimming purposes \ how form a curve % how fly with, 

 against, or across a breeze ? how project itself from a rock directly into space, 

 or how elevate itself from a level surface by the laboured action of its wings ? 



The wing of the bird is elevated to a certain extent in flight by the reac- 

 tion of the air upon its under surface ; but it is also elevated by muscular 

 action — by the contraction of the elastic ligaments, and by the body falling 

 downwards and forwards in a curve. 



That muscular action is necessary is proved by the fact that the pinion 

 is supplied with distinct elevator muscles' 5 ' — nay, more, that the bird can, and 

 always does, elevate its wing prior to flight, quite independently of the air. 

 When the bird is fairly launched into space the elevator muscles are assisted 



* C. J. L. Krarup, a Danish author, gives it as his opinion that the wing is elevated by a vital 

 force, viz., by the contraction of the pect oralis minor; this muscle, according to him, acting with \ th 

 the intensity of the pectoralis major (the depressor of the wing). He bases his statement upon the 

 fact tbat in the pigeon the pectoralis minor or elevator of the wing weighs Jth of an ounce, whereas 

 the pectoralis major or depressor of the wing Aveighs fths of an ounce. It ought, however, to be 

 borne in mind that the volume of a muscle does not necessarily determine the jDrecise influence exerted by 

 its action; for the tendon of one muscle may be made to act upon a long lever, and, under favourable con- 

 ditions, for developing its powers, while that of another muscle may be made to act upon a short lever, 

 and, consequently, under unfavourable conditions. — On the Flight of Birds, p. 30. Copenhagen, 1869. 



VOL. XXVI. PART II. 5 K 



