EXTERNAL ANATOMY OF INSECTS. 431 



not appear to have been noticed, unless it be synonymous 

 with the intermaxillary arcade of Marcel de Serres a . 

 Probably a corresponding support to the muscles, &c. 

 may exist, as we have seen it does in Vespa L. b , in many 

 other heads of the different Orders, which have not yet 

 fallen under examination. Many mandibles, as those of 

 the hornet &c, appear to be suspended to the cavity of 

 the head on the inside by a marginal ligament suffi- 

 ciently relaxed to admit of their play : those of the Or- 

 tlioptera, M. Marcel de Serres informs us, are united to 

 the head by means of two cartilages, the outermost being 

 much the shortest, to which their moving muscles are 

 attached. These he considers as prolongations of the 

 substance of the mandible c . The bottom of mandibles, 

 when cleared of the muscles &c, inclines almost univer- 

 sally to a triangular form ; but in some cases, as in the 

 stag-beetle, it is nearly a trapezium. I cannot conclude 

 this subject without noticing the motions of the mandi- 

 bles. What the author lately quoted has said with re- 

 gard to those of the Orthoptera, will, I believe, apply 

 equally well to all the mandibulate orders. " The arti- 

 culation of mandibles with the skull appears to take place 

 by two points solely ; and as these parts only execute 

 movements limited to a certain direction, they may be 

 referred to ginglymus d . — The movements of mandibles 

 are limited to those from within outwards, and from 

 without inwards e ." Whether they are restricted from 

 any degree of vertical motion, has not yet been proved, 

 as the jaws of vertebrate animals move horizontally as 



A Comparaison des Organcs de la Mastication des Orthopteres, 2. 

 b Sec above, p. 407- note b. c Ubi supra, 4. d Ibid. e Ibid. 5. 



