THE MACHINERY OF FLIGHT 



69 



The Tern and the Falcon, on the other hand, have 

 short, deep keels, and therefore short but big and 

 strong flight muscles. Accordingly, their ordinary 

 stroke is short but powerful. It is highly important 

 also that there should be a firm pivot on which the 

 wing may rest as it moves. During part of the 

 wing's down-stroke there must be considerable 



Breastbone and connected bones of Adjutant — actual length of 

 keel 4| inches. CI. : Clavicle ; Co. : Coracoid ; Sc. : Scapula. 



pressure inward, and were the skeleton to give, 

 were it to supply only an unsteady wobbling pivot, 

 vigorous flight would be out of the question. How 

 is the pivot formed ? There is a strong bone, the 

 coracoid, which springs from the front part of the 

 breastbone and points forward and outward. It 



