MAMMALIA— PHYSIOLOGY 433 



stances, impacted feces, or parasitic worms, such as the pin-worm 

 (see p. 90), cause appendicitis. 



The Large Intestine is divided into the ascending colon, the 

 transverse colon, and the descending colon which terminates in the 

 rectum. In the carnivora the large intestine is short; but is well 

 developed with sacculated walls in the herbivora. The human large 

 intestine, five feet long, is estimated to absorb four hundred cubic 

 centimeters of water in twenty-four hours. 



Digestive Action in the Large Intestine.— The contents become 

 slightly acid due to the fermentation of the contents of the intestine. 

 Beneficial bacteria are very important. Absorption is very active. 

 The great absorbent vessels are the veins and lacteah. The lacteals 

 carry chyle to the thoracic duct at the receptaculum chyli. Food 

 passes through the digestive tract of man in a few hours, but takes 

 three days in the horse and five days in the cow. 



Digestion in the Ruminant (Example: the cow). — The cow lacks 

 incisor teeth on the upper jaws and is therefore unable to cut it as 

 she feeds, but rips loose a tuft of grass by pressing the lower incisor 

 teeth against the upper jaw and giving a jerk of the head. After 

 rolling the morsel between the molars a short time it is swallowed 

 down the esophagus to the rumen or paunch. 



The stomach of the cow is large, occupying three-fourths of the 

 abdominal cavity, and holds 45 gallons. It consists of four parts, 

 the rumen^ the reticulum^ and the omasum^ constituting the pro- 

 ventriculi; while the abomasum or " rennet " is the true stomach. 



The esophagus opens into the stomach on a dome formed by the 

 rumen and the reticulum and is continued through the reticulum to 

 the omasum by esophageal grooves. 



The rufnen is partly divided into dorsal and ventral sacs. Large 

 papillae, sometimes reaching a height of one-fourth inch, stud its 

 brownish mucous membrane. The muscular coat reaches a thick- 

 ness of one inch. The food is stored in the paunch till a favorable 

 time for rumination after which it is passed into the reticulum. 



The reticulum, or honeycomb, is the smallest of the four parts 

 and contains mucous folds one-half inch high enclosing four, five and 

 six-sided spaces (honeycomb) as well as many small papillae. At 

 the reticulo-omasal orifice, there are small horny papillae, curved 

 like birds' claws. The muscular coat has two oblique layers. Little 

 balls of food are prepared in the honeycomb cells and then regurgi- 

 tated for thorough mastication and mixture with the salivary secre- 



