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segment. From this the muscle passes upwards and is 

 inserted on the ventral pyloric wall on the outside of the 

 insertion of the inner pair. 



The following muscles dilate the oesophagus : 



Upper Anterior Oesophageal Dilator Muscles (oe.as.} 

 one pair. Each of these muscles arises from the 

 epistoma close to the origin of the upper anterior dilator 

 muscle. Passing backwards and slightly upwards below 

 the latter muscle, it is inserted on the anterior wall of the 

 oesophagus. The muscle is not compact, but is made up 

 of separate strands which diverge as they approach their 

 insertion. 



Lower Anterior Oesophageal Dilator Muscles (oe.ai.}. 

 One pair of very small muscles. Each arises from a small 

 eminence on the posterior part of the epistoma near the 

 middle line. These eminences are behind the origin of 

 the previous muscle. The muscle passes backwards below 

 the previous muscle, and its insertion on the anterior wall 

 of the oesophagus is immediately below that of the 

 previous muscle. 



Lateral Oesophageal Dilator Muscles (oe.l.) one pair. 

 Each of these muscles is made up of three distinct bands 

 of muscle fibres. Near its origin the muscle is compact, 

 but the fibres diverge as they approach the oesophagus. 

 Each muscle arises near the extreme posterior angle of 

 the epistoma and passes inwards below the upper muscle. 

 Its insertion is on the lateral wall of the oesophagus. 



Posterior Oesophageal Dilator Muscles (oe.p.) one 

 pair. Each muscle arises from the top of the pillar-like 

 portion of the endopleurite of the first maxillary 

 segment and passes inwards and downwards. It runs 

 external to the inner ventral pyloric dilator, and crossing 

 over that muscle it is inserted on the posterior wall of the 

 oesophagus. 



