NO. 3 



INSECT HEAD SNODGRASS 



63 



The diplopod mandible consists of a large basal plate, which appears 

 to form an extensive part of the lateral head wall (fig. 17 K, Add), 

 and of a movable terminal lobe mostly concealed in the normal con- 

 dition by the gnathochilarium (Gch). The basal plate is subdivided 

 into several regions, but particularly there is a proximal piece (fig. 

 26 A, Cd) and a distal piece (St), separated by a line of flexibility. 

 The proximal piece is loosely articulated to the head wall by a single 

 point on its dorsal posterior angle (a). The entire mandibular base 

 is slightly movable by its membranous union with the head, but it is 

 not of the nature of a free appendicular structure, since it has no inner 

 wall — it is merely a convex plate in the lateral wall of the head, but 



KL I flee flee a 



.^^:^m^^ /KL 



ij' . " y^ KL ••=*•^- 



fTxair-ii/n-^i-f.. 



flcs 



A B Le- 



Fig. 26. — Mandibles of Myriapoda. 



A, right mandible of a diplopod, Thyropygus (Spirostreptus), dorsal, showing 

 large dumb-bell adductors (KL, KL) from opposite mandibles, united by median 

 tendon (k). B, left mandible of a chilopod, Scutlgera forceps, lateral view. 

 C, right mandible of Sciitigera, dorsal, somewhat diagrammatic. 



a, articulation of mandible with cranium; BP, basal plate of inaudible; Cd, 

 " cardo " of mandible ; flee, cranial flexor of lacinia ; flcs, stipital flexor of 

 lacinia ; /, promoter of mandible ; /, remotor of mandible ; k, median tendon of 

 mandibular adductors ; KL, mandibular adductors, united by median tendon in 

 diplopod (A, k) to form dumb-bell muscle; Lc, lacinia; St, " stipes" of mandible. 



separated from the cranium by a membranous suture. The free ter- 

 minal lobe of the mandible is a strongly chitinized, jaw-like structure 

 with a proximal molar area and terminal incisor point (fig. 26 A, Lc ) . 

 It is hinged by a dorsal articulation at its base with the end of the basal 

 plate. 



So closely do the parts of the diplopod mandible (fig. 26 A) re- 

 semble the cardo, the stipes, and the lacinia of an insect maxilla 

 (fig. 25 A), that the imagination at once sees in the diplopod ja\v 

 an appendage similar to the maxilla, lacking only a galea and a palpus. 

 That the fancied resemblance is real is easily demonstrated by a study 

 of the musculature. 



The musculature of the diplopod mandible consists of muscles that 

 move the appendage as a whole, and of muscles that move the lacinial 



5 



