44 THE COCKROACH : 



The mandibles of the Cockroach are powerful, single-jointed* 

 jaws, each of which is articulated by a convex "condyle" to the 

 lower end of the epicranial plate, and again by a concave 

 " ginglymus" to the clypeus. The opposable inner edges are 

 armed with strong tooth-like processes of dense chitin, which 

 interlock when the mandibles close ; those towards the tip of 

 the mandible are sharp, while others are blunt, as if for crush- 

 ing. Each mandible can be moved through an angle of about 

 30. A flexible chitinous flap extends from its inner border to 

 the labrum. The powerful flexor of the mandible arises within 

 the epicranial vault ; its fibres converge to a chitinous tendon, 

 which passes outside the central plate of the tentorium, and at 

 a lower level through a fold on the lower border of the clypeus, 

 being finally inserted near the ginglymus. A short flexor arises 

 from the crus of the tentorium. The extensor muscle arises 

 from the side of the head, passes through the fold formed by 

 the lower end of the gena, and is inserted close to the outer side 

 of the condyle of the mandible. 



The anterior maxilla) lie behind the mandibles, and like them 

 are unconnected with each other. They retain much more of 

 the primitive structure of a gnathite than the mandibles, in 

 which parts quite distinct in the maxilke are condensed or 

 suppressed. The constituent pieces are seen in fig. 20. There 

 is a two-jointed basal piece, consisting of the cardo (ca) and the 

 stipes (st). The cardo is a transverse plate bent upon itself, and 

 enclosing muscles; it is attached to the outward-directed pedicel 

 of the occipital frame, and carries the vertical stipes. To the 

 side and lower end of the stipes is attached the five-jointed 

 palp (pa), a five-jointed limb used in feeding and in exploration, 

 while the lacinia (la) and galea (go) are articulated to its 

 extremity. The lacinia is internal and posterior to the galea ; 

 it is broad above, but narrows below to a bifid tooth of dense 

 chitin ; its inner surface is beset with a cluster of strong setae. 

 The galea is more flexible, and forms an irregular three-cornered 



* Professor J. "Wood-Mason points out that in Machilis (one of the Thysanura) the 

 mandible shows signs of segmentation, while the apical portion is deeply divided into 

 an inner and an outer half. Ripe embryos of Panesthia (Blatta) javanica are said to 

 exhibit folds which indicate the consolidation of the mandible out of separate joints, 

 while the cutting and crushing portions of the edge are divided by a "sutural mark," 

 which may correspond to the line of junction of the divisions of a biramous appen- 

 dage (Trans. Ent. Soc., 1879, pt. 2, p. 145). 



