NO. 6 



GRASSHOPPER ABDOMEN SNODGRASS 



19 



These muscles in the second segment are similar to those of the third 

 segment (fig. 10 A, lyo, 171). The external dorsals evidently pro- 

 duce a torsion of the adjoining tergal plates on each other. 



i54> i55> ^5^- Ventral muscles (fig. 8). — The ventral muscles of 

 the second segment are the same as those of the first segment and of 

 the segments following the second. They comprise median (154) and 

 lateral (135) internal ventrals, which are sternal retractors, and an 

 external muscle {136) on each side, which is a sternal protractor. 



137-164. Lateral muscles (fig. 9). — The lateral muscles of the 

 second segment differ in many respects from those of the segments 

 following. They comprise an outer and an inner series of tergosternal 



14-23 14-2b IIT 



I ^ 



Fig. 9. — Lateral muscles of the first and second abdominal segments of 

 Dissosteira Carolina, right side, inner view, female. 



A, all muscles in place. B, external lateral muscles of second segment (160, 

 162, 163, 164) exposed by cutting and partial removal of overlying muscles. 



muscles, a pair of tergopleural muscles, and a sternopleural muscle. 

 The inner series of tergosternals includes three muscles. The first 

 (fig. 9 A, 137) arises on the anterior lobe of the tergum and is 

 inserted on the anterior apodeme {Ap) of the sternum ; the second 

 {138) arises on the tergum above the spiracle and has the same in- 

 sertion as 137. The third {139) is a much larger muscle arising on 

 the tergum beneath the edge of the lateral dorsal muscle {130) and 

 inserting on the lateral margin of the sternum. The outer series of 

 tergosternals includes a short muscle (fig. 9 B, 160) from the anterior 

 ventral angle of the tergum to the anterior end of the sternal apodeme, 

 and a broad posterior muscle (A, 161) arising external to the para- 

 dorsal muscle {131) and inserted on the edge of the sternum behind 



