22 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 92 



relatively slender and weak, so that the appendage evidently does not 

 assist greatly in the process of food-taking. Its true function is shown 

 in the great development and complexity of the muscles controlling the 

 scaphognathite, which cause the currents of water to pass continually 

 over the gills. These muscles are attached to a very thick swelling, 

 continuous at its outer end with the skeletal ridge running across the 

 memhrane covering the gill chamber. Its inner course borders the junc- 

 ture of scaphognathite and coxopodite in a crooked and irregular 

 swelling, which finally comes to an end as a cuplike thickening that 

 bounds the outer proximal borders of endopodite and basipodite. This 

 cup gives origin on its inner side to the adductor muscle of the endo- 

 podite and on its outer side to the flexor of the scaphognathite. No 

 tendons are found in any muscles of the second maxilla. There is no 

 levator muscle in this appendage in Callinectes, Astacus, or Pandalus. 



The coxopodite bears two mesal bilobed endites, the anterior of 

 which has been assigned to the basipodite by Brooks and many later 

 writers. There is no distinguishable basipodite present as such in 

 either of the two maxillae in the blue crab, but in both maxillae the 

 coxopodite is so irregularly shaped that its appearance does not sug- 

 gest superficially that it is in reality all one structure. As in the first 

 maxilla, the position of the basipodite in the second maxilla is to be 

 inferred only by the position of the endopodite. This region is so 

 irregularly convoluted and infolded to give sufficient room for inser- 

 tion to the complex and numerous respiratory muscles that the original 

 boundaries between coxopodite, basipodite, scaphognathite, and endo- 

 podite are completely obliterated in the blue crab. In describing the 

 muscles of the second maxilla, no further reference will be made to a 

 basipodite. 



As all the dorsal muscles are missing in this as in all the following 

 segments, the naming of the ventral muscles remaining might appear 

 to be an easy task, but such is not the case. The myological plan of 

 the second maxilla is greatly complicated by the presence of no less 

 than seven respiratory muscles, some of which are extrinsic, some 

 intrinsic. As a matter of fact, the only muscle which permits of an 

 easily descriptive positional name is 60, an anterior inner ventral 

 muscle, musculiis ventralis mesalis, which functions as an adductor of 

 the coxopodite. The remaining extrinsic ventral muscles (fig. 8) are 

 57, promotor; 56', remotor ; 5p, depressor; and 6j through 66, the 

 anterior respiratory muscles. 



The remaining respiratory muscles {6/ through dp), are intrinsic, 

 as are likewise the adductor of the endopodite (61), and the flexor 

 of the scaphognathite {62). 



