. The structure and life of birds . asudden halt; they can adjust it toevery varying breeze, to every currentor eddy that can be turned to addition to the breast muscles,there are many smaller ones whichhelp in these niceties of we consider the number ofthese, each with its special office, eachgiving the wing a slightly differentturn from any other, it is extraordinarythat Professor Marey should state that the muscular apparatus of the bird,like that of the insect, has nothing FlG- 55—Primary „ & wing feather of Heron to do with the course of the wing ; fis?8 than na
. The structure and life of birds . asudden halt; they can adjust it toevery varying breeze, to every currentor eddy that can be turned to addition to the breast muscles,there are many smaller ones whichhelp in these niceties of we consider the number ofthese, each with its special office, eachgiving the wing a slightly differentturn from any other, it is extraordinarythat Professor Marey should state that the muscular apparatus of the bird,like that of the insect, has nothing FlG- 55—Primary „ & wing feather of Heron to do with the course of the wing ; fis?8 than natura!size) 53 T. he outer web is nar- devation and depression are almost the row- 2o4 THE STRUCTURE AND LIFE OF BIRDS chap. only movements which it can Almosteverything beyond the mere up and down motion heattributes to the resistance of the air. It is true thatsome important movements can be set down whollyor in part to this. Still much is left for the musclesto do. Before their position and their working can be. a. b. Fig. 56.—Humerus of left wing. («) lower ; (b) upper , elevator muscle attaches. The point of attachment varies, in distance from theshoulder and from the pra^axial margin. The action remains much the same. F,air foramen ; ld, latissimus dorsi attaches ; gp, great pectoral or depressor ; P3, thirdpectoial. understood, some further account must be given of thehumerus. Its position, even when at rest, is abnormal;it has received a twist at the joint which has left itset differently from the humerus of any other animal,so that you must not use the terms above andbelow, postaxial and praeaxial, before care-fully finding your bearings. In addition to this it1 Animal Mechanism, p. 214, vii FLIGHT 205 so rotates in the course of the stroke furtherbewilderment is apt to arise. When the wing isfolded, what is really the upper side of the humeruslooks partly upward, but mainly towards the may be easily recognised by an unmistakableland
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