ANATOMY. 31 



diately subjected to the chemical action of the bile and pancreatic 

 fluid. Chyme, acted upon by these juices, becomes chyle. Passing 

 through the great length of the small intestines, nearly all of the 

 nourishing parts of the chyle are absorbed, and the residue (remain- 

 der) enters the caecum, which is the water reservoir. (Water re- 

 mains 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 pre- 

 viously 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. 



URINARY 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 (urination). 

 They are the kidneys, ureters, bladder, and urethra, all lined with 

 mucous membrane. 



The Jcidneys are two in number, right and left, situated on either 

 side of the spine, immediately below the lumbar vertebra?. Their 

 action is to secrete the urine from the blood by a process of filtering. 

 Each kidney has a tube or duct, called the ureter, which carries the 

 urine to the storage reservoir, the bladder. This muscular organ, by 

 contraction, discharges the urine, at intervals, through a tube called 

 the urethra, which extends to the head of the penis. 



The normal amount of urine secreted in twenty-four hours and 

 expelled through the penis varies from 3 to 6 quarts. The color 

 in health is yellowish. 



CIRCULATION. 



I Plate VII.) 



The organs which convey the blood throughout the body are 

 the heart, arteries, capillaries, and veins. 



The heart is a hollow organ, made up of involuntary muscles, and 

 inclosed in a serous sac culled pericardium; it is situated between the 

 lungs, in the thoracic cavity, and averages about 6£ pounds in weight. 

 It is divided into two parts, right and left, separated by a muscular 

 wall. Each part contains two cavities, one above the other, the 

 upper called the auriclt and the lower the ventricle. The cavities are 

 connected by openings, which are guarded by valves to prevent a 

 back flow of the blood. 

 5417—09 3 



