154 REPORT OF COMMISSIONERS OF INLAND FISHERIES. 



THE STOMACH OF THE ADULT LOBSTER. 



The Mouth. 



The mouth of the lobster lies on the lower surface of the head 

 between the mandibles which, when closed, hide the mouth opening. 

 Just in front of the mandibles there is a large median fleshy lobe, the 

 labrum, or upper lip, which forms the anterior margin of the mouth 

 opening. When the mouth is closed, the hinder surface of the labrum 

 projects backward as a median vertical ridge which is prolonged 

 upward through the oesophagus and which makes the mouth V- 

 shaped. The sides of the mouth are formed by a pair of rounded 

 ridges which become higher and converge posteriorly where each 

 ridge expands into a flat boot-shaped plate which is fringed with 

 bristles. These two lobes form the metastoma, or lower lip, which 

 projects downward in the narrow cleft between the mandibles and 

 the first maxillae. The dilation of the mouth is affected by the 

 pulling forward of the posterior ridge of the labrum so that the 

 opening becomes approximately circular. 



The Gilso'phagus. 



The oesophagus is a short vertical canal which passes upward 

 from the mouth between the circumaesophageal connectives and 

 enters the lower side of the stomach. The empty oesophagus is 

 externally cylindrical, except that it is somewhat flattened laterally. 

 The ridge which is a vertical prolongation of the labrum projects 

 backward into the lumen of the oesophagus and makes it trough- 

 shaped (V-shaped) in cross section. 



This ridge is everted forward during dilation of the oesophagus, 

 and so serves to increase largely the size of the oesophagus. 



The Stomach. 



The stomach, in all stages, is divided by an oblique constriction 

 into a capacious anterior storage chamber, the cardiac portion of 



