folsom: mouth-parts of orchesella cincta. 23 



of No. 4. Muscles Nos. 5 and 6 both appear to have the same function, 

 i. e. to protrude and adduct the entire maxilla by pulling upon the cardo. 

 Protrusion may evidently take place until the outer ligament (Plate 2, 

 Fig. 10, lig.) has become tense, whereupon additional contraction would 

 pi-oduce adduction of the maxilla. 



7. Adductor. A stout mass of muscle fibres within the maxilla 

 (Fig. 20, 7. add.) arising along the base of the stipes and inserted ou 

 the lateral aspect of the chitinous expansion (Plate 4, Fig. 31, 7. add.). 

 This large muscle passes under the free dorsal projection of the stipes, to 

 which it does not appear to be fixed. The four muscles numbered 2, 3, 

 4, and 7, which are all attached to the chitinous expansion, which in turn 

 is articulated with the chitinous tendon (bac.) from the head of the 

 maxilla, probably adduct the head of the maxilla by retracting the rod, 

 so that the claws of the head are rotated in a frontal plane toward the 

 claws of the opposite maxilla, in order to meet them and grasp food ; 

 this function of the maxillae seems to be the most important one, judging 

 from the number and size of the muscles which close the claws. 



8. Retractor and adductor. A short muscle on the ventral side of the 

 maxilla (Fig. 21,6". ret. add.), its course also shown faintly in Figure 20, 

 arising on the stalk of the glossa, passing obliquely forward and outward, 

 and inserted on the inflexed lower margin of the stipes. This muscle 

 must retract the stipes and draw it toward the median plane. 



9. Protrusor and adductor. A broad, oblique muscle (Fig. 21, 9. pr't. 

 add.) beneath and running at right angles to the last, also arising on the 

 stalk of the glossa and inserted on the upturned border of the stipes. 

 By this muscle the stipes is protruded and also drawn towards the 

 glossa. 



10. Adductor. A short, stout muscle (Fig. 21, 10. add., Plate 4, 

 Fig. 31) passing directly outward from the stalk of the glossa to the 

 inflexed margin of the stipes. The function of this muscle is clearly 

 to pull the stipes towards the glossa, i. e. to adduct it. 



I believe that the three muscles last described have the important 

 function of abducting the head of the maxilla, or separating the claws of 

 the maxillae preparatory to grasping food. The head of the maxilla is 

 adducted by muscles numbered 2, 3, 4, and 7, which, by retracting the 

 rod, cause the head to rotate upon the end of the stipes. The reverse 

 movement, the opening, appears to be accomplished by the successive 

 retraction and adduction of the stipes by means of muscles Nos. 8, 1, 

 and 10, during which the head rotates upon the end of the chitinous rod 

 until in the position shown in Figures 18 and 19. In this condition the 



