NO. 9 MUSCULATURE OK THE BLUE CRAB COfllKAN 43 



141. ]\Iitscn!iis rcductar propoditis (fig. 13 A). — This muscle arises 

 on the outer and postaxial walls of the carpopodite, narrowing to its 

 tendinous insertion on the posterior proximal horder of the projxxlite, 

 which is moved backward by it. 



142. Mnscuhis abductor dactylopoditis (fig. 13 A). — This rather 

 slender and fcather-sha]:)ed muscle arises in many small fibers on the 

 preaxial wall of the propodite. It is inserted by a very long bladelike 

 tendon on the outer proximal edge of the dactylopodite, which is 

 moved outward by its action. 



14^. Musndus adductor dactylopoditis (fig. 13 A). — Very similar 

 to the preceding in shape and size, this muscle arises largely on the 

 postaxial part of the protopodite and is inserted also on a bladelike 

 tendon to the inner proximal border of the dactylopodite. The termi- 

 nal segment is bent strongly toward the midline by this muscle. 



THE FOURTH PEREIOPOD 



144 a-d. Musculus prouiotor a-d (fig. 12 J). — The first branch {a) 

 originates mesally on the endosternite between the seventh and eighth 

 thoracic segments and is inserted on a heavy tendon attached to the 

 membrane on the anterior border of the coxopodite. The second 

 branch {b) originates dorsally to a on the same endosternite and just 

 below the membrane covering the anteriorly extending promotor 

 muscle of the fifth pereiopod. The branch c originates partly on the 

 lateral surface of the membrane of the promotor of the fifth pereiopod 

 and partly on the endosternite separating the seventh and eighth seg- 

 ments. The branch d originates on the posterior surface of the inter- 

 mediate endopleurite, which in this segment is very small. All these 

 branches are inserted with or beside the first one. The whole muscle 

 moves the leg base forward. 



145. Musculus remotor (fig. 12 L). — As in the three preceding 

 pereiopods, the remotor of the fourth pereiopod is unbranched. It 

 originates on the lower surface of the pleural wall, passing outward 

 and downward to its tendinous insertion on the upper posterior rim of 

 the coxopodite. It opposes the promotor by bringing the leg backward. 



146 a-b. Musculus levator a and b (fig. 12 J, K). — The first branch 

 (a) originates partly on the posterior wall of the endosternite separat- 

 ing the sixth and seventh segments above 14/ a, and partly on the 

 anterior wall of the endosternite separating the seventh and eighth 

 segments. The second branch {b) originates on the anterior wall of the 

 endosternite between the seventh and eighth segments. It would be 

 possible to separate this part into smaller subdivisions, as several 



