lO 



SCIENCE. 



[Vol. XI. No. 257 



comparative anatomists : it is therefore quite possible that even Dr. 

 Coues may learn something from one outside his profession. 



J. S. Newberry. 



New York, Jan. j. 



The communication of Mr. Elliott Coues in the last number of 

 Science, on the mechanism of the flight of birds, renders a response 

 from me, in the interest of science, indispensable. This is the more 

 necessary on account of the unavoidable delay which has occurred 

 in the publication of a paper sent by my son to the Ornithologist 

 and Oologist, and which will appear in the next number of that 

 periodical, and also the delay in the publication of the paper read 

 by me before the National Academy of Sciences, and which has 

 given rise to comment and discussion, and is referred to in Mr. 

 Coues's communication. 



During the last autumn my son, C. C. Trowbridge, who is now a 

 pupil in the Hopkins Grammar School at New Haven, Conn., and 

 who has for several years devoted much of his leisure time to the 

 collection and study of birds, brought to me a hawk which he had 

 shot while it was soaring, and called my attention to the fact that 

 the four outer primaries in each wing were interlocked ; that part 

 of each primary along which the lower margin was cut away lap- 

 ping over or behind the succeeding primary, which was cut along 

 its anterior or upper margin to permit of this interlocking and 

 crossing of these feathers. This was the condition of the wings 

 when he picked up the bird. The general appearances of the wings 

 were so little altered from their ordinary aspects that the interlock- 

 ing would ordinarily escape notice. My son suggested that this 

 interlocking has the effect of relieving the muscular action required 

 for the extension of the primaries during long flights, especially in 

 soaring birds, and, further, that it might aid the bird in steering its 

 way while soaring. 



This discovery seemed to me of much interest ; and after having 

 assured myself by inquiries, and the examination of works on orni- 

 thology, that it had not been made by others, I concluded to bring 

 the subject to the notice of the New York Academy of Sciences, and 

 shortly afterwards read a paper in relation to the same before the 

 National Academy of Sciences. 



I supposed that all lovers of true science would welcome so in- 

 teresting a discovery, even though it was made by a boy. Such, 

 indeed, was the reception of the paper by all the naturalists 

 present ; Professor Marsh, Professor Newberry, and Professor Cope 

 commending the paper, and Dr. Gill, who was not present, but to 

 whom I had exhibited drawings of a wing, and explained the mat- 

 ter, giving encouraging assent to the novelty and importance of the 

 discovery. I mention the names of these gentlemen, because I do 

 not think they will ever have reason or cause to regret their favor- 

 able comments, nor to retract their opinions. 



During many years'study of animal mechanics I have found no facts 

 which exhibit more wonderfully and beautifully than those I have 

 described, the mechanical adjustment of the organs of motion to 

 the medium in which motion takes place, and to the conditions for 

 which provision is made. 



I have in my possession the wings of two large hawks (Biiteo 

 iineatus and Buteo borealis) in which the effects of the habitual 

 interlocking of the four outer primaries has been to wear deep 

 notches, and to produce permanent wrinkles, in the feathers at the 

 point of crossing or overlapping. These I have shown to many 

 scientific men without hearing a doubt expressed of the object or 

 uses of the emarginate cuttings. These long primaries present a 

 serious resistance, with a long leverage, when a bird is soaring, 

 which would overtax the extensor muscles in long-continued soar- 

 ing flights, if not relieved by the process of interlocking. That this 

 interlocking does not impede flight, but in a wonderful and pecul- 

 iar way aids the evolutions of the bird, is evident from the fact that 

 by this interlocking a curvature is given to the anterior edge of the 

 wing, which produces a warped surface, thus enabling the bird to 

 have easy control of the wing with the least possible exertion. A 

 perfectly flat, thin disk, in moving through air, is liable to be vio- 

 lently inverted, or turned broadside to the motion, by the slightest 

 change of angle with the plane of motion. Every one has noticed 

 this when a playing-card is seen to fall through the air. The edge- 

 wise position is one of extremely unstable equilibrium. This would 

 be the condition of the outer part of the wing in soaring, were it 



not for the warped-surface form which, in the wings I have ex- 

 amined, is almost wholly maintained by the interlocking of the 

 primaries, justifying my son's remark that this interlocking is an 

 aid to steering, in soaring flight. 



Mr. Coues, in his communication to Science, disposes of all this 

 matter by a sententious dictum, which, from his extensive knowl- 

 edge of ornithology, must be regarded as an extra-judicial opinion, 

 pronounced with much regret, but with the severe force which sci- 

 ence and truth demand, in the following words : — 



" Much as I regret my absence on those occasions [the meetings 

 at which the papers were read and discussed], I am still more sorry 

 to be obliged to dissent without qualification from the position 

 taken, . . . which is, to my knowledge, quite untenable. . . . With 

 regard to the alleged locking of the primaries : i. It does not take 

 place ; 2. Did it take place, flight would be impossible." And 

 further, " It is fortunate that the mechanism of the wing does not 

 permit the primaries to lock in the manner that has been supposed, 

 for, if it did so, birds could not fly." 



I am necessarily provoked, by these unexplained judgments, to 

 test Mr. Coues's knowledge of the mechanism of the wing which 

 " does not permit the primaries to be locked." I have found, by 

 dissecting the wings of the hawks which I have referred to, that in 

 these birds ten muscles are concerned in the movements of that 

 part of the wing which corresponds to the human hand. Among 

 these are three muscles, with their tendons, which have for their 

 object solely the extension and flexion of the four or five outer pri- 

 maries. The extensor muscles lie between the radius and ulna of 

 the fore-arm, but the tendons run through the wrist-joint and along 

 the hand to the joints of what corresponds in the human hand to 

 the fore-finger, acting solely to extend the four or five primaries be- 

 yond any extension which they could otherwise have. 



The flexor muscle lies in the hand, — a very small muscle, — 

 with its tendon so attached that its only use is to flex the four or 

 five primaries through the small angle by which they are extended 

 by the opposing muscles just described. These muscles are not 

 referred to, nor described, in Mr. Coues's admirable and voluminous 

 work on ornithology, and I beg that he will inform the readers of 

 Science where specific descriptions of these particular muscles, and 

 their uses, can be found. 



There are two other muscles whose tendons are so attached to 

 the joints of the wrist, in the specimens I have, that when the wrist 

 is extended or flexed by the larger extensors and flexors, a partial 

 rotatory motion outwards and inwards may be given to the whole 

 hand. May I ask Mr. Coues where I can find specific descriptions of 

 these muscles, and their uses ? These several muscles are prin- 

 cipally concerned in the mechanism which does permit of the lock- 

 ing of the primaries. 



Mr. Coues discusses another matter in his communication which 

 has only a very general bearing on this question of the primaries. 

 It is the automatic or concomitant extension and flexure of the 

 wrist in birds when the elbow is extended or flexed. In the speci- 

 mens which I have examined, I have found an inelastic tendon, 

 without a muscle attached, fastened at one end to the humerus at 

 the elbow, and at the other to the hand at the wrist, which is an 

 essential feature in this purely kinematic combination. Moreover, 

 this tendon, or string, plays another important part in acting as a 

 string to the bow of the ulna, and taking the strain which might 

 break the ulna, when the bird strikes the air strongly, but for this 

 remarkable support. This is not referred to in Mr. Coues's work, 

 and I would ask him where I may find its description. 



Finally, will Mr. Coues explain ivhy birds cannot fly when a few 

 inches in length of the outer primaries lap over and behind others ? 

 Mechanically this makes a very strong wing, admirably adapted to 

 soaring flight, for which it is evidently intended ; and in one in- 

 stance, at least, which I have given, the bird did apparently fly very 

 well and very naturally with its primaries thus interlocked. 



Moreover, from my own experiments with wings, both before 

 dissection and after the muscles and tendons have been exposed, so 

 that they might be operated by hand, I am convinced that the in- 

 terlocking of the primaries is a simple and easy operation, entirely 

 under control of the bird, and with many birds is habitual. 



W. P. Trowbridge. 



