THE INSECT HEAD SNODGRASS 



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sented by small groups of fibers (fig. 21 B, KLt) arising on the 

 tentorium, or at the base of the hypopharynx. Since the mandibles 

 usually do their hardest work with the inward movement, the dorsal 



mlrp. 



FiGDBK 21. — Mouth parts and tentorium of a cricket, Oryllus assimilis 

 A, labrum and muscles, anterior view. B, right mandible and muscles, posterior 

 view. C, right maxilla, posterior view. D, hypopharynx and labium, lateral 

 view. E, tentorium, dorsal view. F, labium, posterior view. a', a", a'", 

 articulations of mandible, maxilla, and labium with cranium ; admd, adductor of 

 mandible ; abtnd, abductor of mandible ; Cd, cardo ; CT, corpotentoriura ; DT, 

 dorsal arm of tentorium; Ga, galea; 01, glossa ; Ilphu, hypopharynx; KLt, ten- 

 torial adductor of mandible ; Lc, lacinia ; Lst, labiostipites ; mlra, mlrp, anterior 

 and posterior labral muscles ; Mt, raentum ; Pgl, paraglossa ; Plf, palpifer ; Pig, 

 palpiger ; Pip, palpus ; Pmt, prementum ; PT, posterior arm of tentorium ; .S/nt, 

 submentum ; St, stipes. 



adductor muscles are commonly very large and powerful (fig. 21 B, 

 admd), while the abductors (ah?nd) are small and relatively weak. 

 Both dorsal muscles are generally inserted on apodemal stalks or 

 plates, which are not attached directly to the mandibles, but arise 

 from the articular membrane close to the edge of the mandible. 



