NO. I 



INSECT THORAX — SNODGRASS 



69 



they are clearly elevators of the wings, and in the cicada (fig. 29, B) 

 their great size would indicate that they are the principal wing 

 elevators. 



The thoracic musculature of the Diptera is highly specialized in 

 order to give power and efficiency to the wing movements, but at 



Fig. 30. — Mechanism of wing motion. 



A, direct wing muscles of right fore wing and associated parts in a grass- 

 hopper (Dissosteira). a, tendinous thickening of cuticula uniting basalar 

 sclerites (Ba) with anterior part of wing base ; 2Ax, second axillary ; sAx, third 

 axillary ; first and fourth axillaries removed ; b, tendinous thickening of cuticula 

 uniting subalar sclerite {Sa) with ventral plate (c) of second axillary; Ba, 

 anterior basalare ; c, ventral plate of second axillary ; Cx, coxa of middle leg ; 

 D, muscle of third axillary, flexor of wing ; E, basalar muscle to coxa, with 

 branch (£') to basisternum, extensor and deflexor muscles of wing; F, subalar 

 muscle to coxa, extensor and depressor of wing ; PIR, pleural ridge ; Sa, sub- 

 alare; Tg, tegula; IV, base of fore wing, elevated. 



B, C, D, diagrammatic illustration of action of indirect wing muscles in flight 

 as seen in cross-section of thorax through bases of wings, anterior view. A, 

 dorsal longitudinal muscles, attached to phragmata (see fig. 28) ; C, tergo- 

 sternal muscles; T, tergum. The wings are elevated indirectly (B) by depres- 

 sion of tergum caused by contraction of tergo-sternal muscles ; they are de- 

 pressed (D) by elevation of tergum produced by contraction of longitudinal 

 muscles. 



the same time it is greatly simplified in comparison with that of an 

 orthopteroid insect. In each side of the mesothorax there are three 

 large, oblique dorsoventral muscles which serve as elevators of the 

 wings (fig. 34 D). The first is the ordinary tergo-sternal musclefCj 

 attached below on the basisterntmi ; the second (J) is the remoter 

 of the coxa, attached below on the meron, which in the Diptera 

 becomes a wing elevator through the transfer of the meron of the 



