NO. I 



INSECT THORAX SN0DGRAS3 



67 



of the wing mechanism to be developed by insects ; but, in studying 

 the movements of the wings of other insects, it will be most con- 

 venient to begin with those movements made in the horizontal plane, 

 which are effected principally by the direct muscles. 



The flexion of the wing is easiest to understand. When the wing, 

 the hind wing of a grasshopper for example, is turned back toward 

 the side of the body, the distal end of the third axillary (fig. 27, jA.v) 

 turns upward, inward, and forward, carrying with it the anal area 

 of the wing, which is folded and laid against the side of the abdomen. 

 In life, the beginning of this action results probably from the natural 



Fig. 29. — Muscles of right half of mesothorax of cicada (Tibicina septen- 

 dechn), with metathoracic coxa. 



A, A, position of longitudinal dorsal muscle ; B, oblique dorsal muscle ; C, 

 tergo-sternal muscle; P, thoracic branch of depressor of trochanter of hind leg 

 {Tr) ; Q, coxal part of depressor of trochanter. 



elasticity of the wing base, which latter partially flexes when the 

 muscles of extension are relaxed, but the contraction of the muscle 

 of the third axillary undoubtedly completes the folding, and holds 

 the wing tight against the body in its final position. The anterior 

 part of the wing necessarily follows the anal area, but its movement 

 is acclerated by the articular relations of the axillaries. The median 

 plate (in), affected by the motion of the third axillary, pushes the 

 second axillary (2 Ax) medially and revolves it to a longitudinal posi- 

 tion over the first axillary, as the latter ( lAx) turns vertically on its 

 hinge with the tergum. By these multiple movements in the basal 

 elements of the wing, the anterior veins overtake the anals and are 

 folded above them against the side of the body. The flexion of the 



