292 



COMPARATIVE ZOOLOGY 



nun. 



In structure the stomach resembles the esophagus. 

 The smooth outside coat {peritoneum) is a reflection of 

 the membrane which lines the whole abdomen. The 

 middle, or muscular, coat consists of three layers of 

 fibers, running lengthwise, around and obliquely. The 

 successive contraction and relaxing 

 of these fibers produce the worm- 

 like motion of- the stomach, called 

 peristaltic. The innermost, or mu- 

 cous, membrane, is soft, velvety, of 

 a reddish gray color in man, and 

 filled with multitudes of glands, 

 which secrete the gastric juice. 

 The human stomach, when dis- 

 tended, will hold about five pints ; 

 that of the kangaroo is as long as 

 its body. 



The intestinal canal in mammals 

 begins at the pyloric end of the stom- 

 ach, where there is a kind of valve or 

 circular muscle. Like the stomach, 

 FIG 2 55 -vertical section ft varies greatly, according to the 



of the Coats of the Stomach : & J ' 



d, surface of mucous mem- nature of the food. It is generally 



brane, and mouths of gastric , , . ,, - it r i i 



follicles; m, gastric tubuii, longest m the vegetable feeders, and 



or follicles; mm, dense con- shortest in the flesh feeders. The 

 nective tissue; sm, sub-mu- 

 cous tissue; cm, transverse greater length in the former is due 



muscular fiber; lm t longi- 

 tudinal muscular fibers; to the fact that vegetable food re- 



s, fibrous, or serous, coat. ^.^ ^ ^^ ^ f()r di g estion> 



and that a greater bulk of such food is required to 

 obtain a given quantity of nutriment. The intestines 

 measure 150 feet in a full-grown ox, while they are 

 but three times the length of the body in the lion, 

 and six times in man. Save' in some lower forms, as 

 the whales, there are two main divisions, the "small" 

 and "large" intestines, at the junction of which is a 



