NO. 6 GRASSHOPPER ABDOMEN SNODGRASS 21 



ijo, iji. External dorsal muscles (fig. loA). — External dorsal 

 muscles occur in segments // to VII of both sexes, and also in seg- 

 ment VIII of the male. They take their origins on the posterior parts 

 of the terga within the intersegmental folds, and are inserted on the 

 overlapped anterior margin of the tergum following in each case. The 

 median external dorsal of segment /// (figs. lo A, ii B, 770) arises 



167b-. 



167c 



167d 



Fig. 10. — Muscles of the third abdominal segment of Dissosteira Carolina. 



A, muscles of the right side, inner view. 16/, median internal dorsals ; 16S, 

 lateral internal dorsal ; 169, paradorsal muscle ; i/O, median external dorsal ; 

 17T, lateral external dorsal ; 17^, median internal ventral ; 173, lateral internal 

 ventral ; 174, external ventral ; 175, 176, internal laterals ; 177. 178, 179, external 

 laterals; td, attachment of dorsal transverse (diaphragm) muscles. 



B, position of the muscles in cross-section of third segment, diagrammatic. 

 dil, lateral internal dorsals ; dim, median internal dorsals ; DS, dorsal sinus ; 

 DV, dorsal blood vessel ; lAp, lateral apodeme of sternum ; ilc, first ex- 

 ternal lateral muscle ; // , internal lateral muscle ; />. paradorsal muscle ; PvS, 

 perivisceral sinus; td, dorsal transverse muscles (of dorsal diaphragm); tv. 



•ventral transverse muscles (of ventral diaphragm) ; vil, lateral internal ventral 

 muscle; vim, median internal ventral muscle; VNC, ventral nerve cord; VS. 

 ventral sinus. 



dorsal to the lateral muscle (///) ; the first proceeds dorsally to its 

 insertion, the second ventrally. In the posterior segments the corre- 

 sponding muscles become much longer ; the base of the median muscle 

 has migrated ventrally, that of the lateral muscle dorsally. until the 

 two muscles cross each other obliquely on the side of the terguni. 

 The relations of the two muscles to each other and to the successive 

 terga on which they are attached is best seen when the terga are pulled 

 apart (fig. 11 C). The external dorsals in Acrididae, as already noted, 



