1328 



CRUSTACEA. 



muscles moving the basal joints of each of the legs. More minute 

 particulars may be obtained by reference to the figures on Plate 93. 



The muscles moving the cup have not been satisfactorily deter- 

 mined. A slightly elevated line passes from each side with a curve 

 into the membrane of this organ, which may be muscular; if so, they 

 act in flattening the cup preparatory to its attachment. 



The anterior antennae have two extensors and one flexor. The 

 two extensors are inserted in a tendon occupying the anterior margin 

 of the base. They extend half way to the eyes ; one (a, fig. h and 

 fig. a), above the flexor of the anterior cephalic segment, is attached to 

 the upper shell; the other (a', fig. a), much the smallest, passing 

 under the same muscle, is attached below. The flexor (b, figs, h and 

 a) is inserted near the outer part of the base, by means of a short 

 tendon, and is attached near the base of the preceding muscles. 

 These organs have but little motion, and are seldom observed in 

 action. 



The elevators of the buccal mass are four short narrow muscles, 

 inserted in the bony processes, g (figs, p or p 5 ), and attached to the 

 teguments below, under the anterior extremity of the mouth; the 

 insertion of one is exactly posterior, and of the other, a little lateral, 

 as is represented in fig. lp 5 . By means of these muscles the buccal 

 mass may be elevated to a right angle with the surrounding parts. 

 On dying, the mouth is often left in this elevated position. A muscu- 

 lar band passes across the back part of the buccal mass, and after 

 attaching itself to the curved process,/ (fig. p), on each side, con- 

 tinues on, and is inserted in the shell. At c (fig. h), near the eyes, 

 we observe the attachment of a pair of muscles, which are in action 

 when the buccal mass moves; we have not detected their insertion, 

 but suppose, from their position, that they act in depressing it. 



The internal parts of the mouth which receive distinct muscles are 

 as follows :— the upper lip, the mandibles, and the inner parts of the 

 mouth. The upper lip is provided with two pairs of retractors, which 

 are attached near the centre of the exterior membrane of the mouth. 

 The interior pair are very slender ; they are inserted in a minute pro- 

 cess near the extremity of the lip (fig. p 5 ), and move merely the extre- 

 mity, giving it the position in fig. p\ The exterior pair are four times 

 the width of the interior; they are inserted near the middle of the lip, 

 and retract this organ nearly to the bony arch. 



The mandibles are provided with muscles of extraordinary length 



