64 SMITHSUMAN MISCELLANEOUS COLLECTIONS VOL. 8l 



lobe. As in the insect maxilla, the muscles that move the entire organ 

 include a tergal promoter and a group of ventral adductors. The 

 promoter (fig. 26 A. /) arises on the wall of the cranium dorsal and 

 posterior to the articulation of the basal plate with the head. It is 

 inserted on the dorsal (anterior) margin of the distal division {St) 

 of the basal plate, and in its point of insertion alone does this muscle 

 differ from the promoter of the insect maxilla, which is inserted en 

 the edge of the carde (fig. 25 C, /). Functionally, however, the two 

 muscles are the same, and a shift in the point of attachment is not a 

 morphological difference. 



The adductor muscles of the diplopod mandible consist principally 

 of a great mass of fibers (fig. 26 A, KL) filling the cavity of both divi- 

 sions of the basal plate (Cd and St). These muscles are clearly the 

 homelogues of the adductors of the cardo and the stipes in the insect 

 maxilla (fig. 25. KLcd, KLst), which have their origins on the ten- 

 torium, or on the hypepharyngeal apodemes. In the diplopod mandi- 

 bles, however, the fibers of the adductor muscles converge medially 

 from each jaw upon a large, tough, transverse ligament (fig. 26 A, k), 

 and the two conical fiber masses, together with the connecting liga- 

 ment, form a great dumb-liell-shaped muscle uniting the two man- 

 dibles. The two sets of fibers pull against each other to close the jaws. 

 Clearly, the inner ends of these muscles have become detached from 

 the hypepharyngeal apodemes. and the fibers from opposite sides have 

 been united across the middle of the head by means of a transverse 

 ligament. There is also, however, a small group of adductor fibers to 

 each mandible (not seen in the figure) that still retains a connection 

 with the corresponding apodeme of the hypepharynx. Besides the 

 mandibular muscles, other muscles have their origin on the transverse 

 ligament, including muscles to the gnathochilarium, which is either the 

 united second maxillae, or the combined first and second maxillary 

 appendages. In the Diplopoda, therefore, the ventral adductors of all 

 the gnathal ap]')endages have lost their sternal connections by their de- 

 tachment from the hypepharyngeal apodemes. This is a specialized 

 condition, and the ligamentous bridge en which the muscles arise has 

 no relation to the insect tentorium. 



The muscles of the free terminal lobe of the diplopod mandible 

 (fig. 26 A./,r) include a muscle inserted directl}- on the base of the 

 lobe (fics) arising within the stipes (St), and a large cranial muscle 

 (Hcc) arising on the dorsal wall of the head and inserted by a strong, 

 chitineus apodeme on the inner basal angle of the lobe. These muscles 

 corresijond exactly with the lacinial flexors of the insect maxilla, one 

 of which (fig. 25 C. tJcs) arises wnthin the stipes, the ether (tlcc) en the 



