. The structure and life of birds . athers are spread ! The radius, as I haveexplained, slides back when the forearm is extendedand pulls the hand with it, bringing it into line withthe arm. Then follows the sudden expansion of thewing feathers like a fan, effected by means of elasticligaments through which the primary and secondaryfeathers pass, and which are stretched directly theanele between the hand and forearm is widened. Thesystem of ligaments is elaborate. If the skin is removedit will be seen that each of the great feathers is fastenedto the bone by a stringy tendinous mass. Even inth
. The structure and life of birds . athers are spread ! The radius, as I haveexplained, slides back when the forearm is extendedand pulls the hand with it, bringing it into line withthe arm. Then follows the sudden expansion of thewing feathers like a fan, effected by means of elasticligaments through which the primary and secondaryfeathers pass, and which are stretched directly theanele between the hand and forearm is widened. Thesystem of ligaments is elaborate. If the skin is removedit will be seen that each of the great feathers is fastenedto the bone by a stringy tendinous mass. Even inthe dry skeleton they leave their mark. The elasticligaments can be made out without any , through which the quill of each feather passes,can be clearly seen extending from the extremity ofthe handbone or metacarpal to the armpit, including,therefore, all the secondaries, and, with the exceptionof those that spring from the fingers, all the is in fact a continuation of a tendon connected with VII FLIGHT 199. 200 THE STRUCTURE AND LIFE OF BIRDS chap. a muscle that arises from the ribs. A little nearer thebases of the quills there is another ligament which,instead of being pierced by them, runs along the lowerside only. These two ligaments, according to Alix, get confounded at the hand and elbow,but in Pigeons I have found them running still separatebeside the hand. The above description may possibly have given theimpression that the bones and ligaments suppliedsome motive power. This can only come from forearm is put into line with the humerus bymuscular effort, and the effort required is greater sincethe hand is necessarily extended by the same move-ment, and the extension of the hand requires moreforce since it involves the stretching of the ligamentsin which the feathers are set. Thus, indirectly, thehand and the great feathers are prepared for flight bythe action of the triceps muscle that extends the fore-arm. This must not be s
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