THE AiniV HORSE. 33 



The next step, deglutition or swallowing, is mechanically 

 performed l)v I he tongue, pharynx, and esophagus. 



AVlien the food reaches the stomach it is subjected to the next 

 step, maveratioiu a mechanical rolling, mixing, and soaking 

 with the gastric juice. During maceration the gastric juice 

 acts chemically upon other components {nitrogenous parts), 

 rendering them absorbable. Food in the condition in which it 

 leaves the stomach is called eliynie. 



In the small intestines the villi take up the absorbable parts 

 already prepared, and the remaining nourishing parts are im- 

 mediately subjected to the chemical action of the bile and pan- 

 creatic fluid. Chyme, acted upon l)v these juices, becomes ehyle. 

 Passing through the great length of the small intestines, nearly 

 all of the nourishing parts of the chyle are absorbed, and the 

 residue (remainder) enters the ca:vum, which is the water reser- 

 voir. (Water remains in the stomach of the horse only a short 

 time and then passes promptly through the small intestines into 

 the caecum.) 



The residue, soaked in water, gives up, in its passage through 

 to the rectum, the small amount of nutritive matter that has 

 not previously been absorbed. By means of muscular cross 

 ridges in the floating colon the effete material is mechanically 

 molded into pellets of dung, which are stored in the rectum, 

 whence they are ejected, at intervals, through the anus. The 

 ejection is called defecation. 



URIXARY SYSTEM. 



(Plate VI.) 



The organs of this system secrete effete material in the form 

 of a watery fluid, called urine, and expel it from the body. 

 They are the hidneys, ureters, 'bladder, and urethra. 



The Ixidneys are tAvo in number, right and left, situated on 

 either side of the spine, immediate!}^ below the lumbar verte- 

 brae. Their action is to secrete the urine from the blood b}^ a 

 process of filtering. Each kidney has a tube or duct, called the 

 ureter, which carries the urine to the storage reservoir, the 

 hladder. This muscular organ, by contraction, discharges the 

 urine, at intervals, through a tube called the urethra, which ex- 

 tends to the head of the penis. 



The normal amount of urine secreted in twenty-four hours 

 and expelled through the penis varies from 8 to G quarts. The 

 color in health is vellowish. 



