516 



COLLEGE ZOOLOGY 



of two parts, the first being highly glandular 

 and the second a grinding gizzard; two in- 

 testinal ceca are present. The teeth of the 

 cat are highly specialized for seizing prey, 

 and cutting flesh, and a short cecum (no 

 appendix) opens into the intestine. Plant- 

 eating mammals in general have large stom- 

 achs and large and long intestines, often 

 with large ceca, for storing and digesting the 

 enormous quantity of food necessary for 

 their proper nourishment. The 4-chambered 

 stomachs of ruminants are especially inter- 

 esting. Flesh-eating mammals, on the other 

 hand, are provided with smaller digestive 

 organs, their food being more concentrated. 



The digestive system 

 and digestion in man 



More is known about the digestion in 

 man than about any other animal. All 

 animals probably digest their food in a 

 similar manner, that is, the process of di- 

 gestion is, in general, the same throughout 

 the animal kingdom from amoeba to man. 

 The human digestive system resembles that 

 of other vertebrates more closely than it 

 does that of invertebrates; but even in such 

 lowly animals as the earthworm, the organs 

 that constitute the digestive system are given 

 the same names as those in man, such as 

 mouth, pharynx, esophagus, stomach, intes- 

 tine, anus, and digestive glands. The parts 

 of the digestive tract in man are as follows 

 (Fig. 378): 



1. Mouth cavity, containing (1) tongue, (2) 

 openings of ducts of salivary glands, and 

 (3) teeth. 



2. Pharynx or throat cavity, shaped like an 

 inverted cone. 



3. Esophagus, a muscular tube about 9 inches 

 long. 



4. Stomach, a saclike dilatation of the digestive 

 tube. 



5. Small intestine, a muscular tube about 23 

 feet long, and from 1 to IV2 inches in 

 diameter: duodenum, about 1 foot long; 

 jejunum, about 8 feet long; ileum, about 14 

 feet long. 



6. Large intestine, a muscular tube about S 

 feet long and IVz inches in diameter: 

 cecum, a large pouch with vermiform 

 (worm-shaped) appendix, about 3 inches 

 long, at the end of it; colon, the main part 

 of the large intestine; rectum, about 5 

 inches long; anal canal, about IVz inches 

 long. 



The mouth cavity receives the food. Here 

 it is chewed by the teeth, aided by the 

 tongue which helps keep the food between 

 the teeth. The tongue is also a special sense 

 organ of taste and assists in swallowing the 

 food. The mucous membrane lining the 

 mouth contains minute oral glands which 

 pour their secretion into the oral cavity. 

 There it becomes mixed with the secretions 

 from three pairs of salivary glands (Fig. 

 379) and is then known as saliva. Approxi- 

 mately 1000 ml. are produced per day. Secre- 

 tion is an involuntary act stimulated by 

 taste, sight, or smell of food. There are 32 

 permanent teeth as follows: incisors, 8; 



Tongue 



Sublingual duct 



Submaxillary duct 



l*arotid gland 

 Parotid duct 



Sublingual gland 

 Submaxillary gland 



Figure 379. Salivary glands and their ducts. (After Kimber, Gray, and Stackpole.) 



