C A L I G I D E A. 1329 



and power. There are two pairs connected with the same slender 

 bony tendon, the one with its extremity, and the other with its poste- 

 rior side. The former (d, figs, a and li) pass outward and a little 

 downward, and on approaching the apex of the basal joint of the 

 third pair of maxillipeds, curve suddenly backward; they are finally 

 inserted in the margin of the shell opposite the articulation of the 

 head and thorax, after having run over a space equal to one-half the 

 whole length of the cephalothoracic segment. The other pair extend 

 obliquely backward and outward under the base of the maxillae. 

 Although these organs are provided with such remarkable muscles, 

 they are very confined in their motions. They occasionally have a 

 vibratory motion when the animal is nearly exhausted, and this is 

 the only action we have observed. Their position and the form of 

 the adjacent parts satisfy us that their extremities cannot be projected 

 out of the mouth ; and probably they can scarcely reach the opening 

 between the lips. 



On account of the thickness of the enveloping membranes, and the 

 difficulty of dissecting the internal parts of the buccal mass, we have 

 not discovered the muscles moving these parts. We can only specify 

 one pair of slender muscles, which are inserted in the lateral portions 

 of the process, g (fig. p 5 ). It is the retractor of these processes, and 

 through them opens the folds which close the oesophagus, by means 

 of a tendon inserted in the lower extremity of these folds. 



The basal joint of the posterior antennas has but little motion. 

 There are two short muscles, elevating or depressing the extremities 

 of this joint, which we may consider a flexor and an extensor. The 

 flexor, which is inserted near the interior extremity, is directed back- 

 ward and a little outward to its attachment to the lower shell, exte- 

 rior to the base of the following pair of feet. The extensor is inserted 

 at the posterior margin of the joint, and extends obliquely inward, 

 approaching the attachment of the flexor. In the female these 

 muscles have nearly the same position as in the male (fig. b) ; the 

 flexor is inserted near the spines on this joint. The united action of 

 these muscles draws the anterior margin of this joint from the shell. 

 To oppose this motion there is a large muscle inserted near this 

 margin and extending one side below the eyes (e, fig. A), where it is 

 attached to the back shell. 



The extensor of the second joint of this pair of organs is a long 

 broad muscle, attached to the shell above the large curved spine (f, 



333 



