NO. 2 THORACIC MECHANISM OF A GRASSHOPPER SNODGRASS 



59 



MUSCLES OF THE PTEROTHORAX 



The musculature of the wing-bearing segments differs in many 

 respects from that of the prothorax, particularly in the great develop- 

 ment of the dorsal longitudinal muscles (fig. 34, 81, 112), in the pres- 

 ence of large tergo-stemal muscles {8^, 84, iij) and special wing 

 muscles which are lacking in the prothorax, and in the presence of two 

 pleuro-coxal muscles that become wing muscles in the adult. 



The dorsal longitudinals and the tergo-sternals constitute a group 

 known as the indirect zcing muscles because they effect movements of 



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S2 aSpn o^ ^^z 



Fig. 34. — General view of the musculature in the right half of the pterothorax of 

 Dissostcira. Median section, seen from the left. 



the wings by alternate changes in the curvature of the tergum. There 

 is but one special wing muscle in Dissosteira connected with each wing : 

 this is the wing flexor (figs. 37 A, 8j; 49, D), a short muscle hav- 

 ing its origin on the pleuron and its insertion on the third axillary 

 sclerite of the wing base. In many insects there are several small 

 muscles from the upper parts of the pleuron to the edge of the tergum 

 or to the base of the wing, but representatives of these muscles are 

 absent in the grasshopper. The two pleuro-coxal muscles that become 

 important wing muscles in the adult are apparently abductors of the 

 coxa in the nymph (fig. 27 C, M', M"). The first is the pronator- 



