THE ALIMENTARY CANAL. 331 



20 feet long, the large colon holding as much as eighteen 

 gallons of fluid. 



In connection with the digestive tube are several glands 

 whose products aid the digestion of the food. These glands are 

 as follows : salivary-glands (SL), opening into the mouth ; the 

 liver (L), opening into the duodenum ; and the pancreas {Pa), 

 opening into the intestine close to the liver-duct. These three 

 glands are spoken of as true glands. There are others — such 

 as the thyroid, thymus, and sjileen — which have no opening 

 at all ; these are the so-called ductless glands. The salivary 

 glands, of which there are several, are situated in the sides 

 of the mouth and under the tongue ; they are branched glands 

 which pom: out, by means of their ducts, saliva into the mouth 

 to amalgamate with the food. The liver is the largest gland in 

 the body : it consists of several large red lobes closely applied 

 to the diaphragm and wrapping round part of tlie stomach. 

 There can be recognised a right and a left lobe, a middle 

 lobe, and the lobe of Spigelii. By separating these lobes of 

 the liver of a cow or sheep you will observe buried in their 

 midst an elongated, green, thin- walled sac, the gall-bladder. 

 This structure is absent in the horse. Close to it can be traced 

 a tube, the ductus choledochus or bile-duct (Bd), which passes 

 from the liver and runs to the duodenum, into which it opens, 

 — the opening being provided with two flap-like valves, forming 

 the ampulla of Vater. Down this duct the bile runs so as to 

 reach the food. The valves are to stop the flow of food up the 

 bile-duct. In the horse the bile is always flowing into the intes- 

 tine ; in other animals it chiefly flows during digestion — mean- 

 while it is stored up in the gaU-bladder. In the horse the secre- 

 tion is more rapid during digestion, in spite of its constant flow. 



The pancreas (Pa) or "sweetbread" is a pale pink-coloured 

 gland much lobulated, and lies in a membrane in close relation 

 to the stomach and small intestine. From it there runs ofi' a 

 tube, the pancreatic duct (Pd), which opens into the duodenum 

 close to the ampulla of Vater. 



