GENERAL CHARACTERS OF THE VERTEBRATA. 333 



this being effected by a complicated arrangement of muscles, 

 whereby the food is forced down the gullet (oesophagus) to the 

 proper digestive cavity or stomach. In the stomach (fig. 121, 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." Leaving the stomach by its lower 

 aperture (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 sub- 

 jected 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 intes~ 

 final juice, secreted by certain glands 

 situated in the mucous membrane of 

 the intestine itself. 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 in- 

 testine into a tube of larger dimen- 

 sions, 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 use- 

 less remainder being ultimately ex- 

 pelled by an anal aperture. The 

 last portion of the large intestine is 

 usually less convoluted than the rest, 



and IS Called the " rectum." 



The fluid and originally soluble 

 portions of the food, and the chyle 

 which is formed in the process of digestion, are taken into the 

 blood, the losses of which they serve to repair. Part of the 

 nutritive materials of the food is taken up directly by the 

 blood-vessels, and is conveyed by the "vena portse" to the 



s Stomach; sm Small intestine; 

 Itn Large intestine; r Rectum, 

 terminating in the aperture of 

 the anus. 



