126 THE STOCK OWiNEK's ADVISEE. 



SPLEEN. 



The spleen is a soft, reddish-gray organ, situated on the left 

 side of the great curvature of the stomach. It is an exceedingly 

 vascular, ductless gland, having no excretory canal. It weighs 

 from two to four pounds. Physiologists have been unable to 

 demonstrate its use. 



The abdomen and part of the pelvis are lined by peritoneum. 

 The internal surface is smooth, free, moist, and covered by scaly 

 epithelium; it secretes a serous lubricating fluid. A mesentery 

 is a broad, double fold of peritoneum, attached to the abdominal 

 parieties above, and containing a portion of the intestine in its 

 free or remote extremity. 



THE URINARY ORGANS. 



These are chiefly the kidneys, ureters, bladder, and urethra. 

 The kidneys are two compound tubular glands, situated on the 

 right and left of the vertebral column, in the sublumbar region 

 of the abdomen, or under the loins. In the horse they are large; 

 the right one is in advance of the left, lying just behind and 

 beneath the last pair of ribs. They somewhat resemble in shape 

 the heart on playing cards. The kidneys are made up chiefly 

 of the tubes of the gland termed the uriniferous tubes, with 

 blood vessels and nerves and connective tissue. The function of 

 the kidneys is to secrete the urine, a fluid consisting of water 

 holding in solution a varying quantity of earthy salts and a 

 peculiar nitrogenous substance, urea, which, if not eliminated, 

 acts as a blood poison. The urine is secreted by the kidneys and 

 carried off by their ducts, the ureters, to a special reservoir, the 

 bladder, where it accumulates, and from which it is finally ex- 

 pelled at intervals through the urethra. 



The bladder is situated within the pelvic cavity, and when 

 full projecting into the abdomen. It serves as the i-eservoir for 

 the urine, storing it, and at intervals, by contraction of its walls, 

 forcing it into the urethra or excretory tube. It is a musculo- 



