224 



VERTEBItATE ANIMALS. 



in the mouth to the action of a special fluid-^tbe saliva— which acts 

 chemically as well as mechanically upon the food, and which is 

 secreted by special glands, known as the " salivary glands." From 

 the mouth the food passes tlirough a muscular tube — the giillet, or 

 ooiophdfpn (tig. l(i:2, (/) — to the proper digestive cavity, or stomach 

 (.<f). Here it is suljjecteil to the action of a s]iecial digestive fluid — 

 the "gastric juice" — ami is converted into a thick pasty fluid, which 



is called einjme. J>om the stomach 

 the chyme passes into a long con- 

 voluted muscular tube, which is called 

 the "small intestine " (.5;h). Here it 

 is subjected to the action of two other 

 digestive fluids, called the " bile " and 

 " j)a,ncreatic juice," as well as to the 

 fl\iiils secreted liy the intestine itself. 

 The bile is secreted liy a large gland, 

 which is known as the "liver," whilst 

 the ]>ancreatic juice is produced by an- 

 other, termed the " jjancreas," both 

 jjouving their secretion into the iqiper 

 part of the small intestine. By the 

 combined action of these digestive 

 fluids the chj'me is ultimately con- 

 verted into a milky fluid, which is 

 called chi/le, wdien it is ttt to be taken 

 up into the lilood- vessels. The small 

 intestine finally opens into a tube of 

 larger diameter, which is called the 

 "large intestine'' (//")i '^')J this opens 

 on the surface of the body by an anal 

 aperture. In the large intestine the 

 List remaining portions of the food 

 ^^•llich can be rendered useful are ab- 

 sorl)ed into the blood, the indigestible 

 ])ortions beiiig vdtimately got lid of as 

 useless. The fluid ]iroducts of diges- 

 tion (rhijle) are chiefly absorbed from 

 tlie intestinal canal by a set of s])ecial vessels, which ai'e present in all 

 Vertebrates, and which are called the lacteah, from the milky fluid 

 which they contain. These lacteals combine to form a large trunk, 

 by which their contents are idtimatcly added to the circulating 

 blooil. Part of llic ])roducts of digestion is absorbed by the veins 

 wliidi )amify on the intestinal canal, and which ultimately u]iite to 

 form a '_;icat vessel, called the "vena porta-," whicli goes to the liver. 



Fi^. ]tj2. — Digestive systiMU n 

 Maiiiniiil. II Gullet nr .ismpIkil: 

 -s Stuniacli : i^in Small intcMli 

 Im T^aij^'e iulisline ; r Larj^e 

 testiiie ti'i'iiiiiiatiii^^ in its I 

 ]inrti(ni, CLlleil the " reetinji." 



