NO. 9 MUSCULATURE OF THE HLUE CRAR COCHRAN 3I 



proximal jiart of the propoditc and passes quickly to its tendinous 

 insertion on the inner proximal edge of the dactylopodite, which is 

 brought inward and backward. 



THE THH^D MAXILLIl'ED 



This api)endage in the blue crab, as in the crayfish, retains its func- 

 tion of a true mouthpart, and is essentially similar to the second maxil- 

 liped in structure. In the shrimp, on the other hand, the third maxil- 

 liped no longer assists in the taking of food, but is pediform and has 

 completely lost its exopodite, while its endopodite has fewer segments, 

 a characteristic condition in the Caridea. The endopodite in the blue 

 crab is bent inward in its natural position ; in fact, it can not be straight- 

 ened perfectly, owing to the shape of the segments and the uniformly 

 weak development of all the extensors except the one controlling the 

 dactylopodite. 



The coxopodite and the basipodite of the third maxilliped of the blue 

 crab appear to be represented by a single segment, the protopodite. 

 Brooks (1882) has labeled as "basipodite" the narrowed proximal 

 part of the ischiopodite, which externally appears to be set off from 

 the main part of the segment by a suture. An examination of the mus- 

 culature of this segment, however, shows no evidence that it is com- 

 posed of two elements. Furthermore, the exopodite does not originate 

 upon this proximal region of the ischiopodite. which it would naturally 

 do if a true basipodite were involved here. 



pd. Musciilits proniotor III pedis iiiaxillaris (fig. ii).- — This muscle 

 arises mostly on the dorsal side of the endosternite of the third thoracic 

 segment, and partly on the ventral (now anterior) side of the para- 

 phragm, w^hich is very narrow here. It is a powerful and wide muscle, 

 narrowing and thickening as it goes forward to its insertion on a 

 heavy tendinous ligament of the dorsal proximal inner corner of the 

 protopodite, which is moved inward and forward by it. 



p/. Mitsculits rcinotor III pedis iiiaxillaris (fig. ii). — Arising lat- 

 erally on the endosternite. this strong muscle is inserted by a tendon 

 on the lateral proximal edge of the protopodite. It opposes the pro- 

 motor effectively, although it is somewhat less developed. 



p8 a-c. Musculus levator a, b, and c III pedis iiiaxillaris (fig. 

 11). — This muscle is much smaller than the preceding. Its main 

 branch (a) arises on the endosternite beneath the promotor and is 

 inserted near the center of the posterior wall of the protopodite. The 

 shortest branch (b) originates near the main branch on the endoster- 

 nite, and joins the main branch before its insertion on the protopodite. 

 3 



