METABOLISM AND TRANSPORT IN ANIMALS 



515 



Palate 



Mouth cavity 



Tongue 



Pharynx 



Opening of farynx 



Esophagus 



Gal! bladder 

 Liver 



Common bile duct 



Common opening of bile 

 and pancreatic ducts 

 Transverse colon (cut) 



Ascending colon 



Cecum 

 Appendix 



Anal sphincter 



Stomacfi 



Pylorus 



Pancreatic duct 



Pancreas 



Small intestine 

 Descending color* 



Sigmoid colon 



Rectum 

 Anus 



Figure 378. The digestive system of man. 



ceca pour secretions into the midgut. Part 

 of the esophagus of the spider is dilated into 

 a sucking "stomach"; 5 pairs of ceca open 

 into the true stomach, and feces accumulate 

 in a stercoral pocket near the anus. Starfishes 

 specialize in pyloric ceca, a pair of which is 

 located in each arm; two rectal ceca are also 

 present. 



In the amphioxus, pharyngeal grooves, 

 bearing cilia and secreting mucus, aid in 

 carr\ing particles of food into the intestine. 

 A frog is characterized by a sticky pro- 

 trusible tongue, small teeth for holding prey, 

 an esophagus containing folds so that it can 

 be distended to swallow large bodies, and 

 a cloaca into which the excretory and re- 



productive systems, as well as the digestive 

 system, discharge their products. A cloaca is 

 present in many other animals. The intes- 

 tine of the dogfish shark is provided with a 

 spiral valve which furnishes a large surface 

 for absorption and prevents too rapid pas- 

 sage of food. Snakes possess peculiar jaws 

 which can be opened so wide that prey 4 

 or 5 times the diameter of the body can be 

 swallowed. The teeth of snakes are sharp 

 and curved backward; they not only hold 

 prey firmly but force it down the esophagus. 

 Certain teeth in poisonous snakes are 

 grooved or tubular for transfer of poison 

 into a wound. Pigeons and many other 

 birds have large crops; the stomach consists 



