EXTERNAL ANATOMY OF INSECTS. 429 



nominated mandibles (mandibulce) : a term appropriated 

 by Linne to the beaks of birds. The upper-jaws of in- 

 sects this great naturalist named maxilla; — 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 or upper-lip. They are generally powerful or- 

 gans, of a hard substance like horn; but in the Lamellicorn 

 beetles of Mr. MacLeay's families of Scarabceidce and Ce- 

 toniadce, 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 admits a lubri- 

 cous ball projecting from the cheek, upon which it turns a . 



;l A corresponding articulation takes place between the tibia and 

 thio-h of some of the Scarabceidce, which will be hereafter described, 

 See Plate XXVII. Fig. 8— 1 1. 



