VERTEBRATA: GENERAL CHARACTERS. 



453 



ary " glands, the secretion of which serves not only to moisten 

 the food, and thus mechanically assist deglutition, but also to 

 render soluble the starchy elements of the food. The food is 

 next swallowed, or, in other words, is transferred from the 

 mouth to the stomach, this being effected by a complicated 

 arrangement of muscles, whereby the food is forced down the 

 gullet (cesophagus) to the proper digestive cavity or stomach. 

 In the stomach (fig. 244, s) the food is subjected to two sets of 

 actions ; it is mechanically triturated 

 and ground down by the constant 

 contractions of the muscular walls 

 of the stomach ; and it is subjected 

 to the chemical action of a special 

 fluid secreted by the stomach, and 

 called the "gastric juice." This 

 fluid has the power of reducing 

 albuminoid substances to a soluble 

 form, and by its action the food is 

 ultimately reduced to a thick acid 

 fluid, called the "chyme." Leav- 

 ing the stomach by its lower aper- 

 ture (the pylorus), the chyme passes 

 into the intestine, the first portion 

 of which is divided into several 

 sections, but is collectively known 

 as the " small intestine." Here the 

 chyme is subjected to the action of 

 three other digestive fluids ; the bile, 

 secreted by a special organ, the 

 liver ; the pancreatic juice, secreted 

 by another gland, the pancreas ; 

 and the intestinal juice, secreted by 

 certain glands situated in the muc- Fig. 244. Diagram of the digestive 

 ous membrane of the intestine itself. * G 



The result of the whole process is 

 that the " chyme " is ultimately 

 converted into a white, alkaline, 



milky fluid, which is called " chyle." The indigestible portions 

 of the food pass from the small intestine into a tube of larger 

 dimensions, called the " large intestine." Such portions of the 

 food as are still soluble, and capable of being employed in 

 nutrition, are here taken up into the blood, the useless 

 remainder being ultimately expelled by an anal aperture. The 

 last portion of the large intestine is usually less convoluted 

 than the rest, and is called the " rectum." 



.ntestine ; 

 Im Large intestine ; r Rectum, 

 terminating in the aperture of the 

 anus. 



