NO. 2 THORACIC MECHANISM OF A GRASSHOPPER — SNODGRASS 79 



The basal leg muscles arising on the tergum comprise anterior and 

 posterior groups of fibers, or tergal promotors (fig. 43 A, /) and 

 tergal reniotors (/). The tergal promotors are usually contained in a 

 single muscle, which is inserted on the trochantin (B, Tn) when this 

 sclerite is present and well developed, otherwise in the articular mem- 

 brane or on the base of the coxa. The tergal remotors often form a 



b-- 



d A 



Fig. 43. — Diagrams of the cardinal axes of motion in a coxa articulated to the 

 body by a pleural articulation only, and the coxal musculature in a wing-bearing 

 segment. 



A, mechanism of the coxal movements on the pleural articulation (c), inner 

 view. The cardinal movements are: (i) promotion and r emotion on a trans- 

 verse axis (c c) by tergal promoter and remotor muscles (/, /) ; (2) rotation 

 on a vertical axis (d d) by anterior and posterior sternal rotator muscles 

 (K, L) ; and abduction and adduction on a longitudinal axis (b b) hy a. pleural 

 abductor muscle (M), and a sternal adductor muscle (N) arising on sternal 

 apophysis. 



B, diagram of typical musculature of a coxa in a wing-bearing segment freely 

 movable on the pleural articulation. /, promotor of coxa, tergum to trochantin ; 

 /, remotor, tergum to coxa ; K, anterior rotator, sternum to coxa ; L, posterior 

 rotator, sternum or spinasternum to coxa ; M, abductor, episternum to coxa ; 

 M', basalar muscle, basalare to coxa; M", subalar muscle, subalare to coxa 

 (M' and M" are pleural abductors of coxa in the nymph, fig. 2y C) ; N, adductor, 

 sternal apophysis to coxa. 



group of muscles. In Dissosteira the tergal promotor is a single muscle 

 for each leg: that of the prothorax (fig. 23 A, 62) is inserted on the 

 trochantin (Tn) ; that of the middle leg is inserted by an apodeme 

 (fig. 37 A, B, C, 8g) arising between the trochanter and the coxa; 

 whereas that of the hind leg (fig. 38 A, 118) is attached directly on the 

 anterior angle of the coxa (A, D, F, 118). The tergal remotors of the 

 first leg comprise a group of three muscles (fig. 33 A, B, C, D, 6j, 

 64, 6^) inserted on the posterior angle of the coxa ; those of the 

 middle leg include two muscles inserted by apodemes on the posterior 

 angle of the coxa (fig. 37 A, B, po, pi) ; and those of the hind leg em- 



