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masses on either side of the thorax, passing from 

 the dorsal to the ventral body wall. Between 

 these bundles there is a space, in the lower portion 

 of which lies the alimentary canal, main air tubes, 

 and other structures. The upper portion of the 

 space is occupied by a second series of large 

 muscular bundles, passing from the front to the 

 back of the thorax. Neither of these large masses 

 of muscle are inserted directly into the wings, the 

 up and down movement of the wings being 

 caused by alterations in the shape of the thorax, 

 consequent on the contractions of the vertical and 

 horizontal fibres, respectively. 



There are, however, a few fibres arising from 

 the lateral portions of the thorax, and inserted 

 about the base of the wings. 



Leg Muscles. — These occupy but little space 

 in the thorax. They rise, to a large extent, from 

 the internal processes of the exoskeleton (apodemes), 

 and are inserted into neighbouring portions of 

 the limbs. They arise, also, from one segment of 

 a limb and are inserted into another. 



The Muscles of the Body Segments. — These 

 arise from one segment and are inserted into the 

 next. They are arranged dorsally and ventrally 

 in lateral groups throughout the abdomen. 



A small muscle is also situated on each side, 

 passing vertically from the tergum to the sternum. 

 These on contracting flatten the abdomen. 



Muscles in Association with the Alimentary 

 Canal. — Several important muscular masses are 

 connected with the large chitinous pumping organ. 

 A pair of muscles arises from the occipital region 

 of the exoskeleton, and is inserted into the upper 



