136 



the wind near the surface and a short distance ahove it ; and this, again, is an explanation of why an 

 Albatros keeps so close to the surface of the sea, only just topping the waves and occasionally rising hicdi 

 in the air. 



The foregoing sketches (figs. 1-4) are copied from enlarged photographs, the only good ones out of many 

 failures. The difficulty of photographing flying birds from the deck of a rolling ship, often vibrating consider- 

 ably, is great, and I have also found that the sea makes a very bad background ; my most successful attempts 

 were therefore made at birds above the horizon. 



In this connection I ought to quote an interesting paper by Sir James Hector, F.K.S., ' On 

 the Anatomy of Flight of Certain Birds ' * : — 



The means by which the Albatros maintains its remarkable flight for long periods and at all various angles 

 to the wind without any apparent recovery of its initial velocity by the flapping of its wings bas been the 

 subject of much controversy. It has always appeared to me that it might not be altogether a subject in the 

 domain of mathematical physics, as has been assumed, but rather that it might be a difficulty for the anatomist 

 to solve with his scalpel. In 1871 I made some attempts, assisted by my friend, Sir Walter Buller, to dissect, 

 after injecting the arteries and veins, the wing of the Albatros, conjecturing that, as such birds are rarely 

 obtained in the flesh in the Northern Hemisphere, some structural differences might have escaped notice. We 

 were not very successful on that occasion, excepting that I believe we discovered that the long tendon extend- 

 ing from the extensor muscles that control the folding-up and expansion of the wing {extensor plica alaris) 

 terminated in tendinous fibres which, supplemented by muscular fibres, grasped the quills of the large pinion- 

 feathers, and might perhaps impart to them a reciprocal motion like the feathering of an oar. It was difficult 

 to conceive how these muscles could perform two such difficult functions as were involved in the expansion of 

 the wing as a whole and at the same time to exercise a control over its distal appendages. I was therefore 

 not surprised when the result of the dissection of several fine specimens in the flesh preserved in spirit, and 

 which I submitted through Sir Walter Buller to authorities in London, pronounced against there being any 

 unusual anatomical structure present. 



Lately I have had an opportunity of re-examining the wing of a large Albatros in the flesh, and find the 

 following peculiarities, which, so far as I know, have not been hitherto recorded : the extensor muscular 

 tendon, instead of being attached as in other birds only to a fixed process at the distal extremity of the 

 humerus, is also attached by a subsidiary offset to a projecting patelloid bone which is articulated with the 

 process, and thence proceeds to the radial carpal bone, and thence onward along the radial aspect of the 

 manus, where it expands into fibrillse that embrace the quills. When the wing is fully extended, the thrust of 

 this projecting process on the elbow-joint causes a slight rotation of the ulna on the humerus, so that the joint 

 becomes locked, which renders the wing a rigid rod as far as the wrist-joint. At the same time the slight play 

 permitted by the articulation of the patelloid bone on the process allows of the transmission of the muscular 

 pull from the shoulder to the manus without unlocking the joint. By this mechanism the sustaining diameter 

 of the bird is enormously increased without any increase of weight. In an Albatros of ordinary size the rigid 

 surface presented to the atmosphere like a parachute would have an extension of 10ft. Beyond this on either 

 side is the true efficient pinion of the bird, erroneously called the tip of the wing, which, as all who have 

 closely watched the flight of this wonderful bird know, is ever in motion, sometimes flapping on the surface of 

 the sea as it dips to a wave, or elevated as it turns in the force of the gale, and, though no doubt difficult to 

 observe, it is in constant quiver of slight rotation of the broad plumes, opening and closing like Venetian 

 blinds. We have in the mechanism thus described a sufficient source to sustain the prolonged, and to the 

 casual observer apparently effortless, flight of the Albatros. The locking of the elbow-joint in the Albatros is 

 exactly analogous to the locking of the knee-joint of the human skeleton by which man maintains without 

 fatigue that erect attitude which proclaims his supremacy. 



It is very much to the point that the only other bird which possesses a patelloid bone controlling the 

 elbow-joint as the patella does the knee-joint is the Penguin, and in this case the wing-bones have also to be 

 kept rigid during the Penguin's flight under the water. 



* Trans. N. Z. Inst., vol. xxvii., pp. 285-287. 



