STRUCTURE OF MOUTH. 77 



mandibles in my former volume, and there given a drawing 

 (PL 10, fig. 1) of them. There are four muscles : first, the 

 depressor muscle, which is the largest, and is attached, at its 

 upper end, to ligamentous apodemes under the free toothed 

 portion of the jaw; and at its lower end, spreading considerably 

 out, is attached to a concavity close above the basal margin 

 of the labrum ; to understand the action of these muscles, it 

 should be borne in mind that the mandible almost faces 

 the labrum. Tn some genera, as in Coroimla,* the swelling 

 near the basal margin of the labrum (PL 26, fig. 3, k), caused 

 by the internal concavity for the above muscle, is conspicu- 

 ous. The depressor muscle is opposed by a small elevator, 

 attached to the mandible close by the depressor; thence 

 it runs upwards, and is united at its upper end to the base 

 of the palpus, at the point where the latter adheres to the 

 labrum : I have ventured to call this muscle the elevator, 

 from being apparently so well fitted for this purpose ; but 

 I feel some little doubt, from having observed an apparent 

 slight movement in the palpi of living Balani ; and this is 

 the only muscle entering those organs. The free part of 

 the mandible is articulated on a square, thickened piece of 

 membrane, forming part of the side of the mouth (PL 26, 

 figs. 3, 4, c l ; and PL 10, fig. \,a, b, in my volume on the 

 Lepadidae) ; to this square piece of membrane, two short 

 muscles are attached, one above the other, and which ought, 

 in the Plate in my former volume, to have been represented 

 crossing the depressor muscle at nearly right angles ; at 

 their further ends they are attached to about the middle of 

 the labrum, where, at least in Coronula (PL 26, fig. 3, i), a 

 slight concavity can be detected. The action of these two 

 muscles must be to draw the whole mandible against the 

 labrum ; and the depressor muscle might, at the same time, 

 draw the toothed edge downwards, and thus force any prey 

 into the oesophagus. 



The inner maxillae are likewise furnished with four muscles, 

 very nearly as figured in my former volume (PL 10, fig. 10); 

 namely, two muscles, one inside and the other outside the 

 curious apodeme, which in the Balanidae (PL 26, fig. 7, V) is 



* This is figured by Burmeister iu his ' Beitrage zur Naturgeschichte der 

 Itankenfiisser,' Tab. 2, fig. 6. 



