894 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



downwards and forwards, and is inserted on the front part 

 of the pyloric ossicle. 



Outer Posterior Gastric Muscles (g.p.e.) — two pairs. 

 The two muscles at each side iun together so that they 

 may be mistaken for a single muscle. They arise from 

 the under side of the nasogastric region of the carapace, 

 some distance in front of the origin of the dorsal 

 pyloric dilator muscles, but not so near the middle line. 

 They pass downwards, forwards and inwards, and are 

 inserted on the external face of the exopyloric ossicle. 



The above three sets of muscles are concerned in the 

 working of the gastric mill. In addition to these the 

 intrinsic muscles — the cardio-pyloric muscles — to be 

 described later, are also used in connection with the 

 gastric mill. 



The following muscles serve to dilate the fore-gut : — 



Upper Anterior Dilator Muscles (a.s.) — one pair. Each 

 arises from the inner side of the cephalic sternum 

 immediately behind the orbit. The muscle is not a 

 compact one, but passes backwards, upwards and inwards 

 as a series of muscular strands which gradually diverge. 

 They are inserted on the anterior and outer corner of the 

 fore-gut. 



Lower Anterior Dilator Muscles (d.ai.) — one pair. 

 These are a smaller pair of muscles than the preceding. 

 They are very close to the middle line so as to appear 

 almost as a single median muscle. Each arises on the 

 upper side of the epistoma near the middle line and passes 

 backwards and slightly upwards, being inserted on the 

 lower part of the front Avail of the fore-gut near the 

 median line. As in the preceding case, the muscle is 

 composed of several separate strands which diverge as 

 they approach the point of insertion. 



Antero -lateral Dilator Muscles (d.la.) — one pair. 



