132 THE GENITO-URINAEY SYSTEM. 



(1) Kidneys. (2) The ureters. .(3) The bladder. (4) 

 the urethral canal leading from the bladder and communicat- 

 ing with the outside of the animal body either by passing through 

 the penis, or, as in the female, by an opening on the floor of the 

 vaginal cavity. 



If a horizontal section is made of a kidney it will be found 

 to possess a cavity called the renal basin, which receives the urine 

 as it is secreted by the gland. It is here that the ureter com- 

 mences. The internal surface of the renal basin is covered with 

 a mucous membrane, which extends continuously through the 

 ureters to the bladder, which organ it entirely lines, extending 

 from it down the urethral canal to the end of the penis, or, in the 

 female, the vulva. 



The intimate structure of the kidney is composed of liiinute 

 tubes which arise from tufts of blood vessels. The excremen- 

 titious matters are separated from the blood in these tufts and 

 conveyed down the tubes to the renal basin, from which they 

 are conveyed by the ureters to the bladder, being voided from 

 that organ in accordance with the will of the animal. 



The urine is a peculiar fluid. Its solids represent the waste 

 from tissue change. It is the sewage of the system, and con- 

 tains among its solid ingredients a substance termed urea, which 

 if separated and purified appears in the shape of needle-like 

 crystals, which are soluble in hot or cold water. Urea is sup- 

 posed to arise from excess of nitrogenous food, and from nitro- 

 genous changes constantly taking place in the body. Its elimina- 

 tion from the system is very important. Should urea remain in 

 the blood, or be re-absorbed, uraemic poisoning is produced, a 

 condition frequently seen in cases where the functional propei'- 

 ties of the kidneys are impaired by disease. In the ram the 

 urethra is of considerable length, extending as it does the whole 

 length of the penis; just below the anal opening it forms an 

 acute angle to confo*'m with the downward and forward direction 

 of the penis. 



