68 



The Scaphognathite (figs. 27, 28) has a complex 

 movement, and the plane of motion is roughly at right 

 angles to its long axis. There are two sets of muscles — 

 extensors which pull the organ downwards, and flexors 

 which draw it up again to its natural position. In the 

 upward movement the scaphognathite does not remain flat, 

 as when in a position of rest, but it becomes curved so that 

 the upper side is concave. This is effected by a set of 

 accessory muscles. The latter extend into the leaf-like 

 portion of the scaphognathite, and do not stop at the edge 

 of the organ, as do the other muscles. 



All the flexors arise from the anterior face of the 

 last cephalic endopleurite. Their names have been given 

 according to the position of insertion on the scapho- 

 gnathite. The flexors are inserted on the anterior wall 

 of the base of the scaphognathite. 



Inner flexor (i. e. s.) A long narrow muscle 

 arising from the upper part of the endopleurite. It 

 passes down the latter and, turning slightly inwards, it is 

 inserted on the innermost part of the base of the scapho- 

 gnathite. It has a small branch which arises from the 

 side of the epimeron. 



Older flexor (p. e. s.) An extremely broad muscle, 

 which arises immediately beneath the origin of the 

 previous muscle and also on its inner side. It passes 

 down the endopleurite parallel to the epimeron, and is 

 inserted on the extreme outer edge of the base of the 

 scaphognathite. 



Outer median flexor (o. m. e.) A long and fairly 

 broad muscle, arising from the extreme inner border of 

 the endopleurite above the large foramen of the latter. It 

 passes downwards and outwards across the front of the 

 foramen, and is inserted on the base of the scaphognathite 

 on the inner side of the previous muscle. 



