NO. I 



INSECT THORAX — SNODGRASS 



89 



tion and reduction, and elevation and depression, respectively. Joints 

 of the first type are provided with prodiictor and reductor muscles; 

 those of the second type with levator and depressor muscles. Some 

 writers use the terms " flexor " and " extensor," or " abductor " and 

 " adductor " as synonymous with levator and depressor, regardless 

 of the nature of the respective movements ; others call that muscle 

 the " extensor " which accomplishes the principal work of the leg 

 segment distal to the joint, and name its antagonist the " flexor." 

 The last system is appropriate for designating function, but for ana- 



Utr Ar 



Fig. 39. — Diagram of typical leg musculature, left leg, anterior view. 



O, levator of trochanter ; P, Q, thoracic and coxal branches of depressor of 

 trochanter ; R, reductor of femur ; S, levator of tibia ; T, depressor of tibia ; 

 U, levator of tarsus; V, depressor of tarsus; X, X, X, X, branches of depressor 

 of pretarsus (retractor of claws) ; .r, tendon of claw retractor muscles, attached 

 to unguitractor plate (Utr). 



tomical descriptions " levator " and " depressor " are to be preferred, 

 because they lead to no ambiguity and can be applied always to homol- 

 ogous muscles. In the telopodite of the insect leg, only the tro- 

 chantero-femoral joint bends forward and backward, the other three 

 are movable in a vertical plane. 



The muscles that move the trochanter are also levators and de- 

 pressors of the entire telopodite, since the trochanter usually has but 

 little if any motion on the femur. The levator of the trochanter 

 (figs. 39, 40, O) arises in the dorsal part of the coxa and is inserted 

 on the dorsal lip of the trochanter base, usually by a chitinous tendon. 

 The depressor, in pterygote insects, has both coxal and thoracic 



