NO. 9 MUSCULATURE OF THE BLUE CRAB COCHRAN Jl 



inward through the sheetlike sinus tissue, widening somewhat as they 

 approach their insertion along the anterior edge of the hammer-shaped 

 calcification in the posterolateral cardiac plate {Cd PI). (Fig. 30.) 



204 a and b. Musculns dilatator dorsalis pylorici anterior a and b. 

 Two pairs. — The two muscles on each side run close together at their 

 origin, so that they are not readily separable. They arise directly below 

 the origin of the inner posterior gastric muscle (ip8), being attached 

 to the lower end of the same calcareous projection of the inner sur- 

 face of the carapace at the median part of the mesogastric region. Both 

 pairs of dorsal pyloric muscles pass downward and forward as ribbon- 

 like bundles of muscle fibers. The anterior and upper of the two pairs 

 {204 a) is inserted on the anterior pleuropyloric ossicle (XXIII), 

 while the posterior and lower pair {204 b) terminates on the posterior 

 mesopyloric ossicle (XV) ; thus at their insertions they are entirely 

 sej)arate. (Figs. 29, 30.) 



20j a and b. MusaUus dilatator pylorici inferior a and b. Tivo 

 pairs. — Each slender muscle of the outer pair (20^ a) originates on 

 the endopleurite of the first maxillary segment, passing backward 

 and upward to its insertion on the pre-ampullary ossicle {XVIII). 

 The muscles of the inner pair (i'oj b), much longer than the outer 

 but equally attenuate, arise near the base of the mandibular apophysis, 

 thence passing close to the sides of the esophagus and the posterior 

 wall of the cardiac region, and are inserted on the antero-inferior 

 pyloric ossicles (XVII) in the ventral wall of the pyloric region. 

 For the last half of their course, the muscles of this inner pair lie so 

 near together that the two appear to be one. (Fig. 30.) 



The following muscles dilate the esophagus : 



206. Mnsctdus dilatator anterior superior oesopliagei. One pair. — • 

 Each of these muscles arises from the epistome near the midline and 

 just beside the median projection from which spring the basal ocular 

 muscles. Diverging backward and downward, the muscles widen con- 

 siderably at their insertion on the upper wall of the esophagus. (Fig. 

 30.) 



20/. Muscidns dilatator anterior inferior oesophagei. One pair. — 

 These muscles are nearly indistinguishable from the preceding at 

 their origin on the epistome, but they pass straight downward to an 

 insertion in a more anterior position on the esophagus. (Fig. 30.) 



208. Muscidns dilatator lateralis oesophagei. One pair. — This muscle 

 springs from the posterior angle of the epistome, diverging consider- 

 ably as it approaches the esophagus, on the lateral wall of which the 

 various fibers find their attachments, just below those of the preced- 

 ing muscle. (Fig. 30.) 



