NO. 9 MUSCULATURE OF THE BLUE CRAB COCHRAN 45 



pereiopods in that it is branched and also much more strongly developed 

 than in the other legs, owing to the fact that it has to give a powerful 

 backstroke to this fifth leg, which serves as the paddle and which alone 

 causes the very effective swimming movements of the crab. The first 

 branch (a) originates dorsally on a T-shaped part of the endopleurite 

 which is attached mesally on the median plate. The posterior branch 

 (b) originates on the posterior wall of the eighth segment. Both 

 branches are inserted on a heavy tendon attached to the membrane 

 on the proximal postaxial (in this case dorsal) border of the basi- 

 ischiopodite. The muscle as already stated directs the leg backward. 



i^/ a-c. Miisciilus levator a-c (fig. 12 M, N). — The large first 

 branch (o) originates on the median plate just posterior to the first 

 branch of the promotor. It travels laterally beneath the second branch 

 of the promotor and beneath the dorsal half of the remotor also, to 

 its insertion on a heavy tendon attached to the anterior (dorsal) proxi- 

 mal border of the basi-ischiopodite. The second branch (&) is small 

 and weak. It originates on the sternum between the main branches of 

 the promotor and the depressor, and goes upward and laterally to its 

 insertion on the same tendon. The third branch (c) is a heavy and 

 strong one, arising on the sternal wall near to the wedge formed by 

 the first abdominal segment. The entire muscle pulls the leg strongly 

 upward. 



158 a-f. Musculus depressor a-f (fig. 12 M, N, O). — The first 

 branch (a), very large and heavy, originates mesally on the sternal 

 wall of the eighth thoracic segment. Branch b is very small, originating 

 laterally on the sternal wall. Branch c parallels the first branch, begin- 

 ning partly on the sternal wall and partly on the median plate. The 

 fourth branch {d) originates on the posterior sternal wall at the end 

 of the thorax. The fifth and sixth branches {e and /) originate on the 

 dorsal and posterior walls respectively of the coxopodite. All these 

 branches converge upon an extremely heavy tendon attached to the 

 proximal preaxial (in this case posterior) border of the basi-ischio- 

 podite. This extraordinarily powerful muscle pulls the leg base 

 downward. 



i^p. Musculus reductor meropoditis. — See /j/. 



160. Musculus abductor carpopoditis. — See 1^8. 



161. Musculus adductor carpopoditis. — See ijp. 



162. Musculus productor propoditis. — See 140. 

 i6j. Musculus reductor propoditis. — See 141. 



164. Musculus abductor dactylopoditis. — See 142. 



165. Musculus adductor dactylopoditis. — See 14s- 



