296 THE LIVER. 



more than twice or thrice in a day, and the food of the stabled horse being 

 chiefly dry, this water stomach is most useful to him. The caecum will hold 

 four gallons. 



The colon is so? intestine of exceedingly large dimensions, and is capable 

 of containing no less than twelve gallons of liquid or pulpy food. At its union 

 with the caecum and the ileum, although larger than the latter intestine (/), 

 it is of comparatively small bulk ; but it soon swells out to an enormous extent. 

 It has likewise, in the greater part of its course, three bands like the caecum, 

 which also divide it, internally, into the same description of cells. The inten- 

 tion of this is evident, to retard the progress of the food, and to give a more 

 extensive surface on which the vessels of the lacteals may open ; and therefore, 

 in the colon, all the chyle is finally separated and taken up. When this is 

 nearly accomplished, the construction of the colon is somewhat changed : we 

 find but two bands towards the rectum, and these not puckering the intestine so 

 much, or forming such numerous or deep cells. The food does not require to 

 be much longer detained, and the mechanism for detaining it is gradually dis- 

 appearing. The blood-vessels and absorbents are likewise rapidly diminishing. 

 The colon, also, once more contracts in size, and the chyle having been all ab- 

 sorbed, the remaining mass, being of a harder consistence, is moulded into pellets 

 or balls in its passage through these shallower cells. 



At the termination of the colon, the rectum (straight gut) commences. It 

 is smaller in circumference and capacity than the colon, although it will con- 

 tain at least three gallons of water. It serves as a reservoir for the dung until 

 it is evacuated. It has none of these bands, because, all the nutriment being 

 extracted, the passage of the excrement that remains should be hastened and not 

 retarded. The faeces descend to the rectum, which somewhat enlarges to re- 

 ceive them ; and when they have accumulated to a certain extent, the animal, 

 by the aid of the diaphragm and the muscles of the belly, presses upon them, 

 and they are evacuated. A curious circular muscle, and always in action, 

 called the sphincter (constrictor muscle), is placed at the anus, to prevent the 

 constant and unpleasant dropping of the faeces, and to retain them until the horse 

 is disposed voluntarily to expel them. This is effected by the efforts of the 

 animal, assisted by the muscular coat of the rectum, which is stronger than that 

 of any of the other intestines, and aided by the compression of the internal 

 oblique and transverse muscles. 



The larger intestines derive their blood from the posterior mesenteric artery. 

 Their veins terminate in the vena port. 



THE LIVER. 



Between the stomach and the diaphragm its right lobe or division in con- 

 tact with the diaphragm, the duodenum and the right kidney, and the middle 

 and left divisions with the stomach is the liver. It is an irregularly shaped, 

 reddish-brown substance, of considerable bulk, and performs a very singular 

 and important office. 



It has been already stated (p. 217) that the blood, which has been conveyed 

 to the different parts of the body by the arteries, is brought back to the heart 

 by the veins ; but that which is returned from the stomach and intestines and 

 spleen and pancreas, and mysentery, instead of flowing directly to the heart, 

 passes first through the liver. It enters by two large vessels that spread by 

 means of innumerable minute branches through every part of the liver. As 

 the blood traverses this organ, a fluid is separated from it, called the bile. It 

 is probably a kind of excrement, the continuance of which in the blood 

 would be injurious ; but, while it is thrown off, another important purpose 

 is answered the process of digestion is promoted, by the bile changing the 



