98 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 81 



2. — Anterior retractors of the labrum (fig. 37 B). — A pair of long 

 muscles arising on subantennal ridges of frons (fig. 38 D, ;") ; con- 

 verging downward to insertions on base of anterior wall of labrum 

 (%-37B). _ 



J. — Posterior retractors of the labrum (fig. 37 B). — A pair of long 

 muscles arising on subantennal ridges of frons, each laterad of 2 (fig. 

 38 D) ; inserted on dorsal processes of tormae at base of posterior 

 wall of labrum (figs. 37 B, 42 A). 



The articulations of the gnathal appendages occupy typical positions 

 along the lower lateral margins of the cranium. The mandible articu- 

 lates anteriorly with a condyle (fig. 39 A, c) supported at the junction 

 of the epistomal and subgenal ridges {ER, SgR), but projecting on 

 the external surface of the head. Posteriorly the jaw articulates with 

 a facet on the ventral edge of the postgena (figs. 36 C, 39 A, C, a). 

 This articulation as the first is outside the membranous connection 

 of the mandible with the head. The axis of the mandible slopes 

 strongly downward and posteriorly between the articular points. The 

 lateral edge of the mandibular base is separated from the margin of 

 the gena by a narrow, flexible strip of weakly chitinized articular 

 membrane (fig. 36 A, k), at the ventral margin of which arises the 

 abductor apodeme of the mandible (fig. 39 D, 8 Ap). 



The maxilla articulates by a single point on the base of the cardo 

 with a shallow facet on the edge of the postgena (figs. 36 C, 40 C, c) 

 almost directly below the posterior tentorial pit {pt). The maxillary 

 articulation is thus crowded unusually far posteriorly in the grass- 

 hopper. In most generalized insects it lies well before the line of the 

 postoccipital suture, as in a roach or a termite, and is often mucli 

 farther forward. 



The labium is loosely articulated by the elongate basal angles of tbe 

 submentum with the posterior margin of the postocciput at points a 

 short distance above the posterior lower angles of the latter (figs. 36 

 C, 40 C, /). 



The tentorium of the grasshopper has the form of an X-shaped 

 brace between the lower angles of the cranial wall (fig. 39 B). The 

 anterior arms {AT) arise from the lateral parts of the epistomal ridge 

 (ER), their broad bases extending from points above the mandibular 

 articulations half way to the median line of the face. In this respect 

 Dissosteira shows an advance over Periplaneta. in which the bases of 

 the anterior tentorial arms arise from the subgenal ridges and extend 

 only a short distance mesad of the mandibular articulations. 'V\v 

 posterior tentorial arms of Dissosteira (fig. 39 B, PT) arise from the 

 lower ends of the postoccipital ridge (fig. 45 A. PoR). The median 



