NO. 3 



INSECT HEAD SNODGRASS 



139 



4. — The abductor muscles of the mandible (figs. 50 C, 52 B). — A 

 group of fillers, small by comparison with the adductor group, arising 

 on lower lateral and posterior walls of cranium, and on ventral apo- 

 deme of postoccipital ridge laterad of posterior root of tentorium ; 

 fibers converging ventrally, anteriorly, and mesally to insertion on 

 abductor apodeme of mandible. 



5. — The adductor muscles of the mandible (figs. 50 C, E, 52 B, 53 

 E). — An enormous mass of fibers disposed in two sets (figs. 52 B, 

 53 E, 5a, 3b). The fibers of one group arise from almost entire dorsal, 

 anterior, lateral, and posterior walls of corresponding half of epi- 

 cranium above the ocelli (figs. 50 C, E, 53 E, 3a) ; they converge down- 

 ward upon both surfaces of the broad, adductor apodeme of mandible. 

 The fibers of the other group (figs. 52 B, 53 E, 5/;) arise on ventral 

 apodeme of postoccipital ridge (fig. 53 E, vap) mesad of bases of 



Clp 



Fig. 52. — Mandibles of a caterpillar. 



A, mandibles and antennae of Estigmenc acraea, ventral view. B, left mandible 

 of a noctuid, with bases of muscles, dorsal view. 



a, posterior articulation of mandible; Ant, antenna; c, anterior articulation of 

 mandible ; Clp, edge of clypeus ; Mds, mandibles ; 4, abductor muscle of mandible ; 

 ^a, fibers of adductor arising on wall of cranium; 5/', adductor muscles arising 

 on ventral apodeme of postoccipital ridge (see fig. 53 E). 



abductor fibers, and extend horizontally to posterior edge of adductor 

 apodeme of mandible. 



The obliquity of the mandibular axes causes the points of the jaws 

 to turn upward and somewhat posteriorly during adduction. When 

 the mandibles are closed, the teeth on the cutting edges of the two 

 jaws are opposed to each other (fig. 52 A), not interlocked ; but usually 

 one mandible closes first and its toothed edge passes inside that of the 

 other. Live caterpillars examined by the writer always closed the right 

 mandible over the left, and species of several families preserved in 

 alcohol were found to have the jaws in the same position. 



THE MAXILLAE AND LABIUM 



The basal parts of the maxillae and labium are united, and their 

 chitinous areas are reduced or variously broken up into small plates 

 (figs. 51 A, 53 A), which may dififer much in dififerent species. With 



