NO. 9 MUSCULATURE OF THE BLUE CRAB COCHRAN I9 



77. Miisctiliis flexor h palpi iiiaiufihulac (fig. 5 A). — This muscle 

 fills the whole of the first segment of the palp. It arises in the mem- 

 I)rane proximal to this first segment, and is inserted on the proximal 

 joint of the last (second) segment. It lowers this last segment, thus 

 hringing it toward the center. 



THE FIRST MAXILLA 



The first maxilla in the hlue crab, as in the crayfish and shrimp, is 

 flattened, and while it normally lies close to the outer anterior surface 

 of the mandible, it has a considerable degree of freedom of motion. 

 This is due to the fact that its basal part is really in two pieces, the 

 posterior half rather loosely attached to the lower distal margin of 

 the anterior half, and the two halves working together somewhat like 

 the blades in a pair of scissors. The anterior half has been called the 

 basipodite by Huxley, Schmidt, Berkeley, and some other investiga- 

 tors, but since there are no muscles between it and the posterior half, 

 and since the body muscles go to both of them equally, it appears that 

 the structure is in reality a coxopodite, semi-divided and provided 

 with hinges to give necessary pliability. Borrodaile also considers that 

 both parts belong to the coxopodite. It appears that the true basipodite 

 is completely fused with and indistinguishable from the inner border 

 of the coxopodite, as the endopodite arises from this region. 



Three dorsal muscles run to the first maxilla, although it is impos- 

 sible to separate them at their origin because of their extremely attenu- 

 ate form. They separate distinctly into three strands as they pass 

 behind the mandible to their respective points of insertion on the 

 first maxilla. The first of these (fig. 7, 57) is the anterior inner, 

 which may be called musctdus dorsalis anterior mesalis and whose 

 functional name is the anterior adductor of the coxopodite. The next 

 {52) is a posterior inner, musculus dorsalis posterior mesalis, which 

 acts as a posterior adductor to the coxopodite. There is but one outer 

 dorsal muscle, which may be referred to as musculus dorsalis exter- 

 nalis and which functions as an abductor of the coxopodite. 



The ventral muscles may be classed as follows : 



5-/. Upper inner: Musculus ventralis superior mesalis (levator). 



55. Lower inner : Musculus ventralis injcrior mesalis (depressor). 



48. Anterior outer : Mucultis z'entralis anterior externalis (promotor). 



-/(^. Posterior outer: Musculus ventralis posterior externalis (remotor a). 



SO. Median outer: Musculus ventralis medialis externalis (remotor h). 



The only intrinsic muscle in this appendage is ^6, the adductor of 

 the endopodite. 



