THE PIGEON 171 



which enters it just dorsal to the anterior end of the heart. From 

 this point the oesophagus runs forward to the pharynx ; it will be 

 studied later on. 



Study the divisions of the digestive tract posterior to the 

 oesophagus. The glandular stomach and the gizzard are, in birds, 

 equivalent to the stomach of other vertebrates. In the former, 

 digestion goes on ; in the latter, food is ground up and prepared for 

 digestion. The walls of the gizzard in granivorous birds are very 

 thick and muscular, and its cavity is lined with a hard, ridged, 

 cuticular membrane. Note the round red spleen at the side of the 

 glandular stomach. 



The intestine begins at the gizzard and is divided into two por- 

 tions, the small intestine and the large intestine, or rectum. The 

 small intestine is very long. Its anterior portion is the duodenum, 

 which forms the loop inclosing the pancreas and receiving the bile 

 and pancreatic ducts. Its posterior portion falls into two divisions 

 of equal length, the anterior one of which is thicker than the 

 posterior. The anterior end of the rectum is marked by a pair 

 of small sacs, the rectal diverticula; it passes to the cloaca, a 

 short, wide sac which opens to the outside through the anus and 

 also receives the discharges of the urinary and the genital organs. 



The two intestinal glands, the liver and pancreas, have already 

 been studied. 



Exercise 8. Draw the digestive tract so far as observed. 



Cut the stomach from the oesophagus with scissors ; cut the bile 

 and pancreatic ducts and free the stomach, gizzard, and intestine 

 of all their attachments to the liver and other organs, and remove 

 them from the body ; do not disturb the liver. 



Cut open the glandular stomach and gizzard and the duodenum 

 and observe their inner surface. Note the thick walls and the hard 

 cuticular lining of the gizzard. Observe that its cavity can be 

 tightly closed by a valve and shut off from that of the glandular 

 stomach; also that the beginning of the duodenum lies close to 

 the hinder end of the glandular stomach, and that when the giz- 

 zard is closed fluids will pass directly from the glandular stomach 

 into the duodenum. 



