ANIMAL LOCOMOTION. 99 



FLIGHT. 



The flight of the bird is ilhistrated in series 755, 756, 757, 

 pigeon ; 758 to 762, cockatoo ; 763, 764, hawk ; 769, 770, eagle. 

 The following conclusions have been drawn from the photo- 

 graphs : 



The wing is extended upward from the horizontal position by 

 the deltoid and latissimus dorsi muscles to a line which is perpen- 

 dicular to the body, and is quickly again depressed to the hori- 

 zontal position by the pectorals. (See p. 40.) This constitutes 

 the first stage of the " stroke." 



" Recover" is initiated by an inward rotation of the humerus, 

 semiflexion of the wing at the elbow (the pinion remaining ex- 

 tended and directed obliquely downward and outward), and is car- 

 ried well forward to a degree sufficient, when seen in profile, to 

 conceal the head. In this position the primaries are semi-rotated 

 so as to present the least amount of surface to the air in the direc- 

 tion in which the bird is moving. The impetus excited by the 

 "stroke" carries the l)ird upward and forward. In the second 

 stage of " recover" the humerus is rotated outward, the arm is 

 quickly raised, the primaries restored to the position seen in the 

 bird at rest, and the wing is a second time ready for the "stroke." 

 (See p. 38.) 



In the eagle and the hawk the legs are in the position of the 

 " stroke" when the wings are similarly placed. During the 

 "stroke" the legs move backward. This position continues 

 during the "recover" of the wing, so that the time of the "re- 

 cover" is also that of the " recover" of the leg. 



Biological Department 

 University of Pennsylvania, 

 July 1, 1887. 



