ni] THE DIGESTIVE ORGANS 53 



It remains to describe the colon of the horse, in which animal 

 this portion of the gut is better developed than in anj- other. It 

 begins by being very narrow, but rapidly swells out to an enormous 

 size. The first part is high uj) lying a little below the vertebral 

 column and to the right side. It then passes downwards to the 

 floor of the abdominal cavity where it is very large as just 

 mentioned. It next ascends in the direction of the pelvis, and 

 makes a curve of two right angles. The curved part being very 

 small, it then passes forwards and on top of the part already 

 described. Near the diaphragm it passes first downwards and 

 then upwards and backwards again, meanwhile increasing in 

 size to form the enormous double colon ; the calibre of which is 

 greater than that of any other part. Finally it suddenly contracts 

 becoming the single colon. It is obvious that such a large and 

 complicated structure must be of great importance functionally, 

 and there is every evidence that this is actually the case. Its 

 huge capacity, which is five or six times that of the stomach, 

 admits of it retaining great quantities of food substances and 

 fluids which are brought into contact with a large absorptive 

 area of the lining of the gut wall. 



The following are the dimensions of the colon in the domestic 

 animals : 



The Rectum. The faeces consisting of indigestible residue 

 collect in the lower part of the colon and then pass into the rectum 

 from which they are ejected through the anus. In all animals 

 they vary to a greater or less extent according to the diet, and 

 according to the amount of the excretory products of the digestive 

 tract. If no food is given, they consist solely of the latter, and 

 the same statement holds good if the food is completely digested 

 as may happen with the dog when somewhat underfed on an 

 exclusively meat diet. 



In the horse the faeces are generally firm and brownish-red in 

 colour. They contain cellulose, husks of grain, vegetable tubes, 

 starch and fat globules, etc. together with bile pigments and 

 other excretory products. In the ox the faeces are semi-solid 



