xii PHYLUM CHORDATA 507 



The stomach (Fig. 305) is a wide sac, much wider at the 

 end {cardiac), at which the oesophagus enters, than at the 

 opposite or pyloric end, where it passes into the small 

 intestine. The small intestine is an elongated, narrow, 

 greatly coiled tube, the first part of which or duodenum 

 (du and du) forms a U-shaped loop. The large intestine is 

 a wide tube, the first and greater part of which, termed the 

 colon, has its walls sacculated, a structure which is absent in 

 the short, straight posterior part or rectum {ret). At the 

 junction of the small with the large intestine is a very wide 

 blind tube, the ccecum, which is of considerable length and is 

 marked by a spiral constriction, indicating the presence in 

 its interior of a narrow spiral valve. At its extremity is a 

 small, fleshy, finger-like vermiform appendix. 



The intestine, like that of the pigeon, is attached through- 

 out its length to the dorsal wall of the abdominal cavity by 

 a mesentery or fold of the lining membrane or peritoneum. 



The liver is attached to the diaphragm by a fold of the 

 peritoneum. Its substance is partly divided by a series of 

 fissures into five lobes. A thin-walled gall-bladder lies in a 

 depression on its posterior surface. The common bile duct, 

 (c. b. d) formed by the union of the cystic duct from the 

 gall-bladder and hepatic ducts from the various parts of the 

 liver, runs to open into the duodenum near the pylorus. 



The pancreas (pn) is a diffused gland in the fold of 

 mesentery passing across the loop of the duodenum. Its 

 single duct, the pancreatic duct {pn. d), opens into the 

 distal limb of the loop. 



The heart (Fig. 306) is situated in the cavity of the 

 thorax, a little to the left of the middle line, and lies 

 between the two pleural sacs enclosing the lungs. The peri- 

 cardial membrane enclosing the heart consists of two layers, 

 a parietal, forming the wall of the pericardial cavity, and a 



