372 MANUAL OF ZOOLOGY SECT. 



open at the sides the internal apertures of -the branchial 

 clefts and of the spiracle. From this runs backwards 

 a short wide tube the oesophagus (gw/.) which passes 

 behind into the stomach. The stomach is a U-shaped 

 organ, with a long left limb (cd. st.) continuous with the 

 oesophagus, and a short right (pyl. st.) passing into the 

 intestine. At the pylorus the point where the stomach 

 passes into the intestine is a slight constriction followed by 

 a thickening. The intestine may be described as consisting 

 of two parts a narrow anterior and a wide posterior part. 

 The former is very short, only an inch or two in length. 

 The latter (inf.) is longer and is in turn divisible into 

 two portions an anterior and a posterior : the former 

 is very wide and is characterised by the presence in its 

 interior of a spiral valve, a fold of the mucous membrane 

 which runs spirally round its interior, and both retards 

 the too rapid passage of the food and affords a more 

 extensive surface for absorption. The posterior portion 

 (rectum) of the wide part of the intestine differs from the 

 anterior portion in being narrower and in the absence of 

 the spiral valve ; it opens behind into the cloaca. 



There is a large liver (/. /r., r. Ir.) consisting of two elon- 

 gated lobes. A rounded sac fo& gall-bladder lies embedded 

 in the left lobe at its anterior end. The duct of the liver the 

 bile duct runs from the liver to the intestine. Proximally 

 it is connected with the gall-bladder, and by branch-ducts 

 with the right and left lobes of the liver. It opens into the 

 commencement of the wide part of the intestine. 



The pancreas (pan.) is a light-coloured compressed gland 

 consisting of two main lobes with a broad connecting 

 isthmus lying in the angle between the right-hand limb of 

 the stomach and the intestine. Its duct enters the wall of 

 the intestine and runs in it for about half an inch, opening 



