SEA-FISHERIES LABORATORY. 



395 



These are narrow muscle bands each arising about half 

 way along the outer edge of the roof of the pre-branchial 

 chamber. Each passes inwards and downwards parallel 

 to the front edge of the carapace and is inserted on the 

 lateral wall of the cardiac region of the fore-gut, above 

 the oesophagus. 



Postero- lateral Dilator Muscles {dip.) — one pair. 

 These are broad muscles arising near the point of origin 

 of the preceding muscles. Each passes directly inwards 

 and slightly backwards and downwards. The muscle 

 broadens considerably as it approaches the fore-gut. Its 

 insertion is on the anterior edge of the postero-lateral 

 cardiac plate. 



Dorsal Pyloric Dilator Muscles (cl.sup.) — tAvo pairs — 

 anterior and posterior. The two muscles at each side 

 run close together so that it is difficult to distinguish the 

 separate muscles. They arise close together from the 

 under side of the carapace just behind the origin of the 

 outer posterior gastric muscles. They pass downwards 

 and slightly forwards and are inserted on the ossicles of 

 the dorsal wall of the pyloric region of the fore-gut. 

 The anterior muscles are inserted on the posterior meso- 

 pyloric ossicles and the posterior muscles on the uropyloric 

 ossicles. 



Ventral Pyloric Dilator Muscles. Two pairs— outer and 

 inner. Each of the inner pair (i.py.i.) is a long narrow 

 muscle arising near the base of the mandibular apophysis. 

 It passes upwards and slightly backwards on the inner 

 side of the posterior oesophageal dilator muscle and runs 

 very close to the posterior wall of the cardiac region. It 

 is inserted on the anteroinferior pyloric ossicle in the 

 ventral wall of the pyloric region. Each of the outer 

 pair (i.py.e.) is much shorter than the inner pair. Its 

 origin is on the endopleurite of the first maxillary 



