318 



ANIMAL MECHANICS. 



may therefore be applied directly to calculate the work done 

 by the pectoral muscles of birds, round the axis passing 

 through the socket of the shoulder joint, and perpendicular 

 to the plane of the muscle. The maximum work possible 

 would be obtained by placing the socket upon the perpendi- 

 cular to the bisector drawn at the vertex 0, and corresponds to 



Maximum work = 2&Sw sin 0. 



Hence we have, 



Work done . , ^ 



=rz : 7- = Sin (h. (76) 



Maximum work N 



By direct measurement of the angle 0, we obtain the follow- 

 ing Table : — 



Ratio of Work done by the Pectoral Muscle of Birds round the 

 observed Axis pe7'pendicular to its Plane, to the maximum 

 possible Work. 



Bird. 



<P 



s n 0 



Albatross, 





1 1 °.oo' 



0. 190 



Wood pigeon, 





I -55 



0.033 



Heron, 





9 .10 



0. 159 



Macaw, . 





19 .30 



o.333 



Pheasant 





5 -°° 



0.087 





Mean ratio, . . 



. 0'1604 



If we take for the socket of the shoulder the calculated 

 instead of the observed positions, we find by measurement of 

 the angle 0 the following Table : — 



