42 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 92 



jjd a-e. Mitscnlus depressor a-e (figs. 12 G, H, I, 13 A) . — The first 



(a) of the numerous hranches to this muscle originates partly on the 

 posterior wall of the endosternite between the fifth and sixth thoracic 

 segments, partly on the anterior wall of the endosternite between the 

 sixth and seventh segments, and partly on the sternal wall between. It 

 passes to a heavy tendon attached to the tough memljrane bordering 

 the proximal anterior rim of the basi-ischiopodite. The next branch 



(b) begins on the endopleurite between the sixth and seventh segments 

 just above the anterior prolongation of the promotor of the fifth 

 pereiopod. The next branch (c) lies partly behind branch b, originat- 

 ing on the endosternite near its fusion with the endopleurite separating 

 the sixth and seventh segments. Branch d originates anteriorly in the 

 coxopodite, and branch e posteriorly in the same segment. All these 

 are inserted on the heavy tendon or on the membrane beside it. Their 

 mutual contraction pulls the leg base forcibly downward. 



i^/. Musculus reductor meropoditis (figs. 12 I; 13 A). — This fan- 

 shaped muscle begins in several places on the preaxial part of the 

 basi-ischiopodite, and is inserted postaxially on the proximal border 

 of the meropodite. The hinge between these two segments is only 

 slightly developed preaxially, and not much more so postaxially, so 

 that the rearward motion imparted by this muscle is slight. It is 

 opposed by the stiffness of the preaxial connection which causes 

 the leg to become straightened again after its contraction. 



1^8. Musculus abductor carpopoditis (figs. 12 I, 13 A). — This 

 large muscle originates in a great many bundles of fibers attached 

 on the whole dorsal surface of the meropodite from its anterior to its 

 posterior walls. These bundles run together before their insertion 

 on a long bladelike tendon which is inserted on the posterior dorsal 

 proximal border of the carpopodite. This muscle extends the carpopo- 

 dite so that it lies in a straight line with the meropodite. 



ijp. Musculus adductor carpopoditis (figs. 12 I, 13 A). — This 

 originates in the same way as the abductor but lies ventrally in its 

 segment and is inserted similarly by a very long tendon leading to the 

 anterior ventral proximal border of the carpopodite. This muscle is 

 therefore in perfect opposition to the adductor, bending the carpopo- 

 dite at right angles to the meropodite. 



140. Musculus product or propoditis (fig. 13 A). — This densely- 

 fibered fanlike muscle originates on the entire outer border of the 

 carpopodite, its parts coming together on a heavy leaf-shaped tendon 

 which is inserted on the proximal median anterior border of the 

 propodite, to which it gives a strong forward motion. 



