428 EXTERNAL ANATOMY OF INSECTS. 
sects this great naturalist named maxille—and not im- 
properly, since the office of mastication is more pecu- 
liarly their office than that of the under-jaws, which Fa- 
bricius has distinguished by that name: as the term man- 
dible, however, is generally adopted, I shall not attempt 
to disturb it. ; 
The mandibles close the mouth on each side under the 
labrum orupper-lip. They are generally powerful organs, 
of a hard substance like horn; but in the Lamellicorn 
beetles of Mr. MacLeay’s families of Scarabaidu and Ce- 
toniad@, they are soft, membranous, and unapt for masti- 
cation. In Coleopterous insects they commonly articulate 
with the head by means of certain apophyses or processes, 
of which in many cases there are three discoverable at 
the exterior base of the mandibles; one, namely, at each 
angle, and one in the middle. That on the lower side is 
usually the most prominent, and wears the appearance 
of the condyle of a bone: it is received by a correspond- 
ing deep socket (or cotyloid cavity) of the cheek, in 
which, being perfectly smooth and lubricous, it moves 
readily, but without synovia, like a rotula in its aceta- 
bulum. The upper one projects from the jaw, forms 
the segment of a circle, and is concave also on its inner 
face. A corresponding more shallow, or, as anatomists 
speak, glenoid cavity of the cheek, where it meets the 
upper-lip, receives it, and the concave part adimits a lubri- 
cous ball projecting from the cheek, upon which it turns?. 
This structure you will find in the stag-beetle, and some 
other timber-devourers. Other Coleoptera have only a 
* A corresponding articulation takes place between the tibia and 
thigh of some of the Scarabeide, which will be hereafter described. 
See PLare XXVII. Fie. 8—11. 
