340 SPLANCHNOLOGY. 



URINARY SYSTEM. 



The organs of this system secrete the urine from the blood 

 and excrete or expel it from the body. These organs are chiefly 

 the Kidneys, Ureters, Bladder, and Urethra. The urine, which 

 is a watery fluid, 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 expelled, at intervals, 

 through the urethra. 



KIDNEYS. 



The kidneys are two compound tubular glands, situated on 

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



FIG. 120. 



Horizontal section of 'the right kidney, a, Fibrous capsule 

 detached ; 6 b b, Cortical layer ; c c, Medullary layer ; d d d, 

 Cut ends of large blood-vessels; e, Pelvis of the kidney; 

 /, Ureter. 



region of the abdomen, in contact with the crura of the diaphragm 

 and psoe muscles. They are supported by peritoneum and 

 cellular tissue, in which is deposited a quantity of fat ; less 

 perhaps in the horse than in other herbivorous animals. The 

 kidneys are also supported by their vessels as well as by the 

 pressure of the digestive organs ; the right one is in advance of 

 the left, lying just behind and beneath the last pair of ribs, 

 whereas the left one lies about two inches farther back. They 

 somewhat resemble in shape the heart on playing cards, the left 



