430 EXTERNAL ANATOMY OF INSECTS. 
res*. Probably a corresponding support to the muscles, 
&c. may exist, as we have seen it does in Vespa», 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- 
thoptera, 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*. 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 ginglymust.—The movements of mandibles 
are limited to those from within outwards, and from 
without inwards®.” Whether they are restricted from 
any degree of vertical motion, has not yet been proved, 
as the jaws of vertebrate animals move horizontally as 
well as vertically—so those of insects may have some 
motion vertically as well as horizontally; and it seems 
necessary for some of their operations that they should. 
* Comparaison des Organes de la Mastication des Orthopteres, 2. 
» See above, p. 406. note”. ° Ubisupra,4. ‘Ibid. * Ibid. 5. 
