176 INTERNAL ANATOMY OF INSECTS. 
muscle acts upon each extremity of the sinus—these 
branches appear to be tendinous*. The depressors of 
the head are the antagonist muscles to the above, and 
have their attachment to the anéepectus and its antefurca>. 
A circumstance distinguishes these muscles in many Co- 
leoptera, that seems hitherto to have been overlooked. 
If you take the common dung-beetle (Geotrupes sterco- 
rarius), and carefully extract the head with its muscles 
from the trunk, you will see on each side of the depres- 
sors a subovate corneous scale, of a pitch colour’, which 
is attached only to the muscle, and designed to strengthen 
it: if you then examine the anterior cavity of the manc- 
trunk, you will perceive on each side, just within the 
lower margin, a minute triangular scale, of a similar sub- 
stance; these ligaments, like the pax-wax, or ligamenta 
nuche, in mammalia, though in a lower situation, are 
doubtless intended to sustain the action of the muscles. 
With regard to the moveable organs of the head—the 
antenne, maxilla, palpi, tongue, mandibule, &c., have 
each their appropriate apparatus of muscles: but I shall 
only notice those of the last, mandibule. These are 
principally abductors and adductors to open and shut 
them: from the work that the jaws of some insects have 
to do, you may conjecture that they must be furnished 
with powerful muscles. In caterpillars and other larvee, 
in which state the action of the mandibles is most in re- 
quisition, the muscles are what Cuvier calls pennzform4, 
and are attached on each side to a tendinous lamina or 
cartilage. In the grub of Dytiscus the power and mag- 
2 Prare XX Vilyire, 1. a, > Vor. III. p. 368—, 543, 
586. Pirate XXII. Fie 7. Cuv. whi supr. 448. 
> Parr SOXVIl. Bre. 5.70 * Anat. Comp. i. 136. 
