104 M. O. Strobelt on the Anatomy and 



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muscles of the head and thorax, we shall here also distinguish 

 three groups — the muscles which move the individual abdo- 

 minal segments, the respiratory muscles, and the muscles of 



the generative organs. 



Motor Muscles of the Abdominal Seyments. — At the dorsal 

 surface we find in each segment on each side of the median 

 line five longitudinal muscular fasciculi. The fasciculi placed 

 on the two sides of the median line are distinctly separated 

 from each other by an interspace, which widens towards the 

 middle of the body and narrows again towards the extremity 

 of the abdomen. In the first segment the muscles originate 

 at the posterior margin of the segment, and run, somewhat 

 converging, to the hinder margin of the thorax. These are 

 the elevators of the thorax. The muscles of the other seg- 

 ments are always inserted at the hinder margin of the segments 

 in which they are situated, and run to the hinder margin of 

 the next preceding segment. Besides these we find in the 

 third segment another muscle on each side, which originates 

 close to the other five, but runs outwards and forwards to the 

 hinder lateral margin of the second segment. The length of 

 the muscles in the respective segments is as follows : 



millim. 



In segment 1 0*166 



„ „ 2 0-178 



„ „ 3 0-J28 



„ 4 0-269 



„ „ 5 0*288 



„ „ 6 0329 



„ „ 7 0-340 



„ „ 8 0-155 



„ „ 9 0-059 



The ventral surface shows five longitudinal muscles on 

 each side in each of the first seven segments, three on each 

 side in the eighth. Those of the first segment are the depres- 

 sors of the thorax, the others the flexors of the ventral rings ot 

 the abdomen. Their insertion and course in the respective 

 rings is exactly the same as with the muscles of the dorsal 

 surface. In the first segment three more muscles on each side 

 originate near the longitudinal muscles, run outwards and 

 forwards, and are inserted upon the hinder lateral margins ot 

 the thorax. These are the lateral motors of the thorax. 



To the motor muscles of the abdomen we have further to 

 reckon some longitudinal muscles which pass at the lateral 

 margins through the segments from the second to the seventh. 

 There are two pairs of these in each of the above-mentioned 

 segments. Those of the second segment are inserted upon 



