MOVEMENT 



51 



Abd. of coxa 



sclerites, which are thus capable of movement in relation 



to each other (Fig. 17). The segment of an insect's leg 



next the body is the conical or subconical haunch (coxa), 



the broad base of which adjoins the sternal region of its 



segment while it tapers distally 



to its junction with the small 



sickle-shaped trochanter which 



is succeeded by the long stout 



thigh or femur. In some in- 

 sects, cockroaches for example, 



the cuticle of the haunch is 



partly transparent so that the 



strong muscles which, by their 



contraction, move the leg as a 



whole can be seen through it, 



their white colour contrasting 



markedly with the general 



brown hue of the exoskeleton. 



The leg-muscles in the cock- 

 roach are described by Miall 

 and Denny (1886). From the 

 dorsal region of the thorax on 

 either side muscles pass to the 

 inner and outer edges of each 

 haunch ; these are respectively 

 the adductor and abductor coxae, 

 as by contraction of the former 

 the leg is drawn in towards the 

 axis of the body, while by con- 

 traction of the latter it is moved 

 outwards. A very strong muscle 

 with its basal attachment (origin) 

 also on the thoracic skeleton 

 traverses the haunch, its fibres 

 converging to their distal attach- 

 ment (insertion) by means of a tendon on the inner 

 (convex) edge of the trochanter. This is the muscle 

 whose contraction straightens the thigh in relation to the 



€xt. lib. 



R«tr. tan. 



Fig. 17. — Left intermediate Leg 

 of Cockroach (Blatta orien- 

 talis), showing segments and 

 muscles, c, coxa; tr, tro- 

 chanter ; /, femur or thigh ; 

 ti, tibia or shin ; ta, tarsus or 

 foot. Muscles : Add, adductor ; 

 Abd, abductor ; Ext, extensor ; 

 Fl, flexor : Retr, retractor. 

 X3. After L. C. Miall and 

 A Denny, The Cockroach^ 

 1886. 



