MANUAL FOR STABLE SERGEANTS. 27 



35. The anus is a muscular ring forming the posterior opening 

 of the alimentary canal. It appears as a round projection below the 

 root of the tail. 



36. The stomach and intestines are suspended in the abdominal 

 cavity by strong, fibrous bands, the mesentery, which are attached 

 above to the lower surface of the muscle below the spinal column. 

 Accompanying these fibrous bands are blood vessels, lymphatic 

 vessels and glands, and nerves. Inclosing the intestines and lining 

 the abdominal cavity is a serous membrane called the peritoneum. 

 The mesentery is a part of the peritoneum. 



37. In the abdominal cavity are three large glands, the liver, 

 pancreas, and spleen. The spleen is a ductless gland. The liver 

 and the pancreas are part of the digestive system. 



38. The liver lies behind the diaphragm and in front of the 

 stomach. It weighs from 10 to 12 pounds. Its function is to secrete 

 bile, which is poured into the small intestines, where it aids diges- 

 tion. 



39. The pancreas is situated behind the stomach and in front 

 of the kidneys, in the upper portion of the abdominal cavity. It 

 weighs^about 17 ounces. Its function is to secrete pancreatic fluid, 

 which is poured into the small intestine, to aid in digestion. 



40. The spleen is attached to the left side of the stomach. It 

 is reddish gray in color and weighs from 2 to 3 pounds. Its function 

 is not definitely known, but it is supposed to be concerned in the 

 formation and destruction of blood corpuscles. It also appears to 

 act as a reservoir for the extra supply of blood required by the 

 stomach during digestion. 



41 . The abdominal cavity is inclosed by the muscles of the back 

 above, the abdominal muscles on the sides and below, and the dia- 

 phragm in front. In the rear it is continuous with the pelvic cavity. 



PHYSIOLOGY OP DIGESTION. 



42. The function of the digestive organs as a whole is to take in 

 the food, digest it, absorb the nutriment, and discharge the waste 

 material from the body. The various steps are as follows: 



43. Food is taken into the mouth by the lips, prehension, and is 

 there ground up by the teeth, mastication, and mixed with saliva, 

 insalivation. Saliva, which is secreted by the salivary glands, 

 moistens the food and acts chemically upon certain parts. The 

 tongue determines the taste of the food and by its muscular action 



