52 THE BIOLOGY OF INSECTS 



haunch, trochanter and thigh moving as one piece ; the 

 muscle is therefore known as the extensor femoris. It is 

 readily understood that by the straightening of the leg with 

 the foot resting on the ground the body of the insect is 

 thrust forwards ; hence these muscles are of great importance 

 in such actions as walking or running. A smaller muscle 

 {flexor femoris) has its origin along the outer aspect of the 

 haunch and is inserted by means of a tendon on the outer 

 (concave) edge of the trochanter ; when this muscle con- 

 tracts the thigh is bent towards the haunch, a movement 

 which lifts the foot from the ground and draws it forward 

 in preparation for the subsequent repetition of the extending 

 and propelling action. Within the thigh are two muscles 

 whose fibres converge from their origin along the outer and 

 inner edges of that segment to tendinous insertions on the 

 corresponding edges of the base of the next leg-segment, 

 the shin (tibia) articulated to the thigh at the flexible knee- 

 joint ; these muscles are respectively the extensor ^nd flexor 

 tibiae^ their function respectively being to straighten or bend 

 the leg at the knee. Beyond the shin follows the foot 

 (tarsus) with its five segments, the first the longest and the 

 fifth longer than any of the three intervening. A muscle 

 {flexor tarsi) originating along part of the inner edge of the 

 shin has its fibres converging into a long tendon which 

 traverses the successive segments of the foot and is inserted 

 into its tip ; when this muscle contracts the foot is curled 

 or bent by the flexion of all its segments in the same 

 direction. There are also two other muscles in the shin, 

 the protractor and retractor tarsi ; these are inserted at the 

 base of the foot respectively in front and behind, and their 

 action is to swing the foot backwards or forwards in relation 

 to the rest of the leg. The backward swing of the foot 

 clearly assists in the forward propulsion of the body in walk- 

 ing or running. Each foot-segment has a patch of w^hite 

 cuticle below its terminal region ; this gives some power of 

 adherence to smooth surfaces, and the patch {pulvillus) at 

 the tip of the foot is larger and more conspicuous than the 

 others. The terminal foot-segment carries a pair of strong 



