865 



niiisculus pectoralis majoi-, which is fioiu 5 to iü times more bulky 

 than the coraco-brachialis. By pressing the wing down, this powerful 

 niust'le acts more directly in the locomotion, and is quantitatively 

 very differently developed in the different orders according to their 

 mode of flying, most so for the Galiinae and the Columl)idae, which 

 fly rowing (vol ramé), least for the Birds of Prey and the Owls, 

 which mostly fly floaiingly (vol plane), little too for the Marine 

 Palmipeds, which sail through the air in their flight (vol a voile). 

 In connection with this the area of the wing and the volume (or 

 weight) of the principal muscle active in flying, the muscuhis pecto- 

 ralis major are in leversed ratio to each other. To mention only the 

 extremes, the Birds of Prey have on an average double the wing 

 surface of the Galiinae, and their musculus |)ectoralis major has only 

 half the weight. For our purpose it is, however, necessary to know 

 whether also under for the lest equal circumstances, the weight of 

 the latter muscle is proportional to the body weight. If this appears 

 to be actually the case, we may safely conclude that it holds for 

 the whole of the muscles and for other Vertebrates too. Hence we 

 should only compare Birds of the same order, which also resemble 

 each other as much as possible in form and mode of flying, because 

 on account of the presence of two counteracting factors, area of 

 the wing and development of the muscle, deviations of the former, 

 also within a same order, immediately assume great importance for 

 the latter. From Magnan's determinations I have chosen 10 pairs, 

 formed from 20 species of Birds, eacli pair consisting of two species 

 which, though different in size, resemble each other as closely as 

 possible, as regards form of the body and flight, arid calculated the 

 relative body weight (P), the relative weight of the musculus pecto- 

 ralis major (Mp), the relative surface of the body {S, as /^Vj)> «^"^ 

 the relative area of the wing (A) ^), and for (mostly other individu- 

 als of) the same species also the relative weight of the musculuKS 

 coraco-brachialis {Mc). 



When specific and individual deviations are disregarded, theie 

 thus appears to exist a simple proportionality of the weight of the 

 muscles with the weight of the body. In the average values found 

 the weight of both muscles is slightly more than proportional to 

 the body weight; but most probably this is chiefly to be attributed to 

 the circumstance that also the area of the wings becomes on an average 

 somewhat larger in proportion to the surface of the body ; which 



^) A. Ma-gnan, Variations de la surface alaire chez les Oiseaux, l.c , Année 

 1913, NO. 2, p. 119—125. 



