NO. 2 THORACIC MECHANISM OF A GRASSHOPPER SNODGRASS 



15 



appears to be a remotor of the coxa in Scutigera, though it may liave 

 an abductor function also. The ventral median muscles of Scutigera 

 comprise two bundles of fibers, one arising- medially on the sternum 

 (fig. 10 B, N), the other (iV) arising on the lateral arm of the en- 

 dosternal furca. These muscles are coxal adductors since the coxa 

 has no fixed ventral articulation in Scutigera. The ventral coxal mus- 

 cles are covered dorsally by large bands of trochanteral muscles that 

 take their origin on the sternum. 



Fig. II. — Diagram of the basal musculature of an insect leg. 



Bs, basisternum; Cx, coxa; I, tergal promotor muscle: /, tergal remotor; 

 K, sternal promotor (anterior rotator); k, f ureal suture; L. sternal remotor 

 (posterior rotator) ; M, abductor of the coxa; M', M", abductors of the coxa 

 that become the basalar and subalar muscles in the wing-bearing segments of 

 adult insects ; A'', adductor of the co.xa ; SA, sternal apophysis ; Sex, subcoxa ; 

 SI, sternellum ; T, tergum ; Tn, trochantin. 



In the insects the sclerotic areas of the subcoxae of the legs evi- 

 dently become the pleural plates of the thoracic segments. The tergal 

 promotor muscle of the leg base (fig. 11, /) retains its connection with 

 the subcoxa in the more generalized pterygote insects, being inserted 

 on the trochantinal sclerite of the subcoxa (Tn) except when the 

 trochantin is lost, the muscle then having its insertion on the anterior 

 angle of the coxal base. The remotor muscle (J), which may be repre- 

 sented by several fiber bundles, is always inserted on the coxa or on 

 coxal apodemes. The anterior and posterior sternal muscles (K, L) 

 arise on the sterna or the sternal apophysis, or on the spinasternum. 



