8o SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



brace two muscles (fig. 38 A, iig, 120) similarly inserted (D, F). 

 The two sets of tergal muscles, promoters and remotors, are clearly 

 antagonists pulling on opposite extremities of the longitudinal basal 

 axis of the coxa (fig. 43 A, b-b), the fulcrum of which is at the pleural 

 articulation (c). 



The sternal musculature of the coxa, when complete, includes three 

 groups of fibers, one inserted on the anterior angle of the coxal base, 

 one on the posterior angle, and one on the mesal rim. The first two are 

 the anterior and posterior rotators (fig. 43 B, K, L) serving to turn 

 the coxa in the plane of its base (A) on the pleural articulation (c). 

 In the foreleg of Dissosteira an anterior rotator is lacking, but there 

 are two posterior rotators (fig. ;^s C, 66, 6/), the first arising on the 

 base of the sternal apophysis (SA), the other on the spina (iSpn) ; 

 both are inserted on the posterior angle of the coxa (C, D). The 

 middle leg has a single anterior rotator (fig. 37 A, B, p^) and a single 

 posterior rotator (pj), the first arising on the sternellar lobe of the 

 mesostemum (fig. 35, 92), the second (pj) on the spina (2Spn). In 

 the kind leg there is a single, large two-branched anterior rotator of 

 the coxa arising on the metasternum laterad of the base of the sternal 

 apophysis (fig. 35, 121), and inserted on the anterior angle of the coxa 

 (fig. 38 D, 121) ; and there are three posterior rotators (figs. 35, 38 E, 

 122, 12J, 124) all arising from the arm of the sternal apophysis. 



The mesal sternal muscle of the coxa (fig. 43 B, A?^) is the adductor. 

 It pulls upward (A, N) on the inner end of the transverse axis (c-c) 

 of the coxal base passing through the pleural articulation (c). In each 

 segment of Dissosteira the coxal adductor arises on the under surface 

 of the arm of the sternal apophysis (figs. 33 C, 6g ; 37 A, 100, loi ; 

 38C, D, E, F, 7j?o). 



The pleural muscles of the coxa include the functional abductor 

 fibers (fig. 43 B, M) which directly oppose the adductor (N), and, in 

 the wing-bearing segments, two other muscles (B, M', M") that ap- 

 pear to be derived from the primitive abductor system. 



In the foreleg of Dissosteira the abductor of the coxa is a two- 

 branched muscle (fig. 33 D, 68a, 68b) arising on the inner surface of 

 the invaginated episternum (Eps). In the middle leg the abductor 

 group comprises three distinct muscles (fig. 37 A, P4, p§, pd) all 

 arising on the episternum. The first two are inserted by flat apodemes 

 anteriorly on the outer rim of the coxa (B, C, P4, 95) and perhaps 

 function here as accessory promoters. The large third muscle (A, 

 96), however, is inserted close before and distinctly laterad of the 

 pleural articulation (B, c) by a slender apodeme (pd) arising in the 

 coxal corium, and it must be the functional abductor of the coxa. In 



