MOVEMENT 63 



and ginglymus) with the head-skeleton, resembles that of 

 the Eanvig previously described (pp. 17-19). The mandible 

 (Fig. 22) is pulled outwards by its abductor muscle (Ex), 

 which consists of several bundles of fibres arising from the 

 upper lateral region of the head capsule, and converging to a 

 chitinous tendon inserted at the outer edge of the mandible 

 beyond the condyle. The large adductor (L) wliich pulls 

 the mandible inwards to meet its fellow of the opposite side 

 is a much thicker and stronger muscle than the abductor ; 

 its numerous bundles of fibres arise from the top and back 

 of the head-capsule, and converge to a strong chitinous 

 tendon wliich is inserted in the hind inner region of the jaw. 

 Each mandible has also a short adductor (S) whose parallel 

 fibres pass directly from the inner head skeleton (tentorium) 

 to the inner face of the mandible's convex outer wall. The 

 contraction of these two adductors pulls the mandible in 

 towards its fellow, so that the pair of jaws meet, with their 

 teeth interlocking, opposite the centre of the mouth (Fig. 

 22, B), unless some food substance happens to He bet^veen 

 them ; in such case the teeth cut it, and the molar areas 

 grind it into small fragments. 



The outer edge of the mandible has another muscle (In) 

 of small extent whose fibres are fastened to its inner aspect. 

 These converge into a long slender tendon which is inserted 

 into the side of the tongue. This pair of muscles {levator es 

 linguae) serve by their contraction to protrude the tongue. 

 They are opposed by another pair of muscles (retractores 

 linguae) which, passing from the tentorium on either side to 

 the base of the tongue, pull that organ backwards into the 

 mouth (Fig, 22, V). 



The complex structure of the maxillae (see previous 

 chapter, p. 19, and Fig. 23) necessitates a corresponding 

 elaboration in the muscular system by which their parts are 

 worked. Inserted into each cardo is a strap-Hke depressor 

 muscle (IF) with three sections arising from the tentorium. 

 This depressor, by its contraction pulls the cardo and thus 

 the w^hole maxilla downwards. An elevator or abductor (P) 

 runs from the top of the head-capsule (epicranium) to the 



