INTERNAL ANATOMY OF INSECTS. 183 



thus, as the muscle-notches are wide in this insect, the 

 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 antepectus and its antefurca b . 

 A circumstance distinguishes these muscles in many Co- 

 leoptera,, that seems hitherto to have been overlooked. 

 If you take the common dung-beetle (Geotrupes stereo- 

 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 mani~ 

 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 

 nuchtje, 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 

 antenna, maxilla, palpi, tongue, mandibulce, &c., have 

 each their appropriate apparatus of muscles : but I shall 

 only notice those of the last, the mandibulac. 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 larvae, 

 in which state the action of the mandibles is most in re- 

 quisition, the muscles are what Cuvier calls pcnniform*, 

 and are attached on each side to a tendinous lamina or 



a PLATE XXVII. FIG. 1. a. b VOL. III. p. 367-, 541,584. 



PLATE XXII. FIG. 7- Cuv. ubi supr. 448. 



c PLAT* XXVII. FIG. 5. a. d Anal. Comp. i. 136. 



