206 ESSENTIALS OF ZOOLOGY 



posteriorly to form the oesophagus, and almost immediately 

 gradually expands into the elongated stomach. Both the 

 oesophagus and the stomach present tubular glands. The 

 stomach ends distally in a constriction which marks the 

 position and the effect of the contraction of the sphincter 

 muscle of the pylorus. The small intestine at its beginning 

 is directed forwards at a slight angle with the stomach. This 

 is the duodenum, and it receives the pancreatic-bile duct. 

 The lining membrane of the distal part of the duodenum and 



Eus. Corp. ad. Sem.ves. Cloaca 



Post. nor. Cer. hem. \ Cent. Pul. art. Coel. mes. I Ao. Tes. Kidney Uro. Ur. 



Tongue Conus. \ Bile d. St. \ Duo. Spleen Reel. Bladder 



Vent. \ Pan. 



Gall bl. 



FIG. 105. General dissection from the side. 



a great part of the rest of the small intestine is produced into 

 a series of posteriorly directed pocket valves, similar to the 

 semilunar valves of the circulatory organs. The mucous 

 membrane is much folded, and the cells secrete mucus. A 

 sudden expansion of the intestine marks the beginning of the 

 large intestine, and this is directed backwards and upwards 

 to open into the cloaca. 



The liver is developed from the outgrowth of a pit which 

 is formed at an early period in the anterior part of the floor 

 of the primitive enteron. In the adult the liver is resolved 

 into right and left lobes, *and it is incised into subsidiary lobes. 

 The space between the two lobes is occupied by the green 

 gall bladder. It will be observed that the bile duct commences 



