382 DR PETTIGREW ON THE PHYSIOLOGY OF WINGS. 



its breadth, and for the general elegance of its shape {vide figs. 11 and 16, Plates 

 XII. and XIII.) It is especially interesting from the fact that the wing- 

 movements can be more readily and satisfactorily analysed by its aid than by 

 the aid of any other British wing with which I am acquainted. The following- 

 account, taken from a perfectly fresh specimen, may prove interesting. 



The joints of the gannet's wing, particularly the shoulder joint (x of figs. 1G 

 and 17, Plate XIII.) admit of very free movements. When the wing is slightly 

 flexed the under surface of the posterior margin of the pinion can be rotated 

 downwards and forwards until it makes a right angle with the horizon — the 

 greatest angle which it makes in extension amounting to something like 45°. 

 In flexion the elbow (s of figs. 9, 10, and 11, Plate XII.), wrist (t), and meta- 

 carpal joints (v w) admit of a great variety of movements, the forearm (c d) moving 

 on the arm (e /), and the hand {a b) upon the forearm (c d) in an oblique 

 spiral direction from above downwards and from below upwards. The whole 

 pinion, in fact, is flaccid, and the feathers opened up and thrown out of position 

 as shown more especially at figs. 9 and 10, Plate XII. The forearm is folded 

 upon the arm in nearly the same plane {vide x s t of fig. 17, Plate XIII.), the 

 secondary and tertiary feathers (c e g of fig. 9, Plate XII.) being inclined slightly 

 upwards and forwards, so that they form inclined surfaces with the horizon 

 — the secondaries forming an inclined surface which looks inwards and upwards 

 as indicated by the arrow marked c d of fig. 9, Plate XII., the tertiary feathers 

 forming two inclined surfaces, one of which is directed upwards and outwards 

 as indicated by the arrow e /of fig. 9, Plate XII., the other inclining upwards 

 and inwards as shown at g h of fig. 9, Plate XII. The hand rotates upon the 

 wrist (t of fig. 9, Plate XII.,) as upon a hinge, the tip of the wing as it darts 

 out and in describing the segment of a circle (m n of fig. 9, Plate XII.) The 

 hand is folded upon the forearm in such a manner that the anterior margin of 

 the tip of the wing {v w b of fig. 9, Plate XII.) ascends, while the posterior 

 margin (a of fig. 9, Plate XII.) descends. As a consequence the hand and tip 

 of the wing are folded beneath the forearm or body of the wing as indicated by 

 the radius m n of fig. 9, Plate XII. The hand and tip of the wing form 

 with the horizon an inclined surface, which is directed outwards and upwards 

 as indicated by the arrows a b of fig. 9, Plate XII. The upward and outward 

 inclination of the under surface of the outer portion of the wing of the gull is 

 well seen at a b of fig. 12, Plate XII. The tip of the wing, it will be observed, 

 acts during flexion as a true kite from beloiv upivards and from within out- 

 wards^ We have in the flexed wing of the gannet four different sets of 



* The same happens in the wings of all birds, and in the wing of the bat and insect. The out- 

 ward and upward inclination of the tip of the wing is well seen in the beetle. This portion of the wing 

 acts as a true kite, when the wing is being extended or thrust away from the body towards the termi- 

 nation of the up stroke. The under surface of the tip of the wing consequently contributes to flight 

 during the up stroke. 



