lO SMITHSOXIAN MISCELLANEOUS COLLECTIONS VOL. 92 



trolling the various basal parts of the leg are likely to break if enough 

 tension is put upon them to show in what manner they influence the 

 distal segments. Even the coarse and heavy muscles on tendons which 

 do not break cannot invariably be assumed to cause the same motion 

 in the segment of the stiffened dead tissue that they do in the pliable 

 living organism. Thus it frequently becomes very difficult to deter- 

 mine whether a muscle in function is a promotor or an adductor, a 

 remotor or an alxluctor. Coupled with this difficulty is the fact that 

 the crab is so highly specialized away from the ancestral primitive 

 condition that some of the appendages now lie in a partly reversed 

 position, and one appendage, the mandible, is completely reversed. 

 This makes it equally hard to give the muscles positional names accord- 

 ing to their points of attachment, and there are, besides, so many small 

 muscles controlling the basal segments that one soon has to resort to 

 the expedient of giving some of them merely a number, having ex- 

 hausted the available adjectives descriptive of their locations. 



It is possible, however, to divide the muscles according to their place 

 of origin, all the muscles originating on the carapace being called dorsal 

 muscles, and those coming from the ventral surface and the sternal 

 apodemes being referred to as ventral muscles. 



Only those segments anterior to the second maxilla have both dorsal 

 and ventral muscles. The second maxilla and the segments behind it 

 lack dorsal muscles, but are fully equipped with ventral muscles. 



The dorsal and ventral muscles are all extrinsic, meaning that they 

 originate in the body itself beyond the boundaries of the true appen- 

 dage. The intrinsic muscles are contained entirely within the appen- 

 dage itself and control the distal segments of the limb and the flagellum 

 if one be present. 



As far as it has seemed possible to do it, I have followed the nomen- 

 clature adopted by Schmidt and later by Berkeley, in their respective 

 anatomical analyses, to facilitate comparison between the three forms 

 involved. The muscles of the blue crab do not always present perfect 

 analogies in either position or function to those of the crayfish and the 

 shrimp, however, and where a difference in function seems possible, 

 the positional name may be given as first choice, with Schmidt's or 

 Berkeley's corresponding name in synonymy. When so many muscles 

 were found that the positional name of the one in question could not be 

 given with the use of only one or two qualifying adjectives, the whole 

 muscle has been referred to merely by its number. It is not well to be 

 too arbitrary in assigning definite names to some of the more obscure 

 muscles of the blue crab until such time as other representatives of the 



