20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 94 



/5p. The two tergopleural muscles (B, 162, 163) arise anteriorly and 

 posteriorly on the lower part of the tergum external to 159 and 161, 

 and converge upon a narrow linear sclerite in the membrane between 

 the tergum and the sternum. In all the other segments the external 

 lateral muscles are attached directly on the sternum. The sternopleural 

 muscle of the second segment is a group of very short fibers (B, 164) 

 connecting the pleural sclerite with the sternunL 



i6s, 166. Muscles of the spiracle (fig. 9B). — The dilator of the 

 spiracle {16^) is a long slender muscle arising on the apodeme of 

 the sternum, the occlusor {166) a short muscle arising on the tergum ; 

 both are inserted on the manubrium of the movable valve of the spi- 

 racular atrium. 



MUSCLES OF THE THIRD SEGMENT 



The musculature of the third segment presents the typical abdominal 

 musculature of the grasshopper, since its pattern is repeated in seg- 

 ments /// to r// in both sexes, and its dorsal and ventral muscles 

 are duplicated in the second segment. 



/d/. Median internal dorsal muscles (fig. 10 A). — These muscles 

 of the third segment, as those of the second, consist of four flat groups 

 of fibers {a, h, c, d) lying within the pericardial chamber, extending 

 from the anterior tergal ridge {tr) to the anterior edge of the fol- 

 lowing tergum. In the succeeding segments they become more oblique 

 (figs. 8, 12, 182, ip/, 22/') with their posterior ends dorsal to their 

 anterior ends. 



168. Lateral internal dorsal muscle (fig. 10 A). — The lateral dorsal 

 muscle is separated from the median dorsals by the attachments of 

 the transverse muscles of the dorsal diaphragm on the tergum (td), 

 and is, therefore, extrapericardial. In the following segments this 

 muscle becomes conspicuously fan-shaped (figs. 8, 12, i8_^, ip8, 228, 



243)- 



i6g. Paradorsal muscle (fig. 10 A). — The paradorsal muscle is dis- 

 tinguished from the other lateral dorsal muscle {i6y, 168) by the 

 fact that it lies external to the internal lateral muscles {175, 176). 

 It has the same relations in some other insects, though it is a muscle 

 not generally present. In Dissosteira it is repeated in the segments // 

 to VII of both sexes, and in segment VIII of the male (fig. 12, 244). 

 The paradorsal muscle has been termed a " pleural " muscle, but it 

 lies well within the area of the dorsum. Since it occurs in some larval 

 insects lacking tergal plates, the writer here discards the former name 

 of " paratergal " muscle. (Snodgrass, 193 1.) 



