Excretion. 57 



ters. The bladder is the urinary reservoir situated iu 

 the pelvic cavity, although when full it may extend into 

 the abdominal cavity. It is divided into a fundus (the 

 wide part) and neck which is continuous with the ure- 

 thra, the latter the tube carrying the urine to the out- 

 side of the body. The exit from the bladder is guarded 

 by a circular (sphincter) muscle, which by its-contraction 

 prevents the trickling of urine continuously. The coats 

 of the bladder are three in number, serous — externally, 

 muscular or middle coat — and mucous — internally. The 

 urethra in cattle and sheep differs from that of the horse, 

 in the former having an S-shaped curve, whereas in the 

 latter it is straight. The urethra in the female of these 

 animals opens on the floor of the vulva, at a short dis- 

 tance (3 to 4 inches) from the outside of the body. In 

 cows the entrance to the urethra is guarded by a valve- 

 like piece of skin, which must be lifted in order to pass 

 the catheter. The difference in length and construction 

 of the urethra in the sexes accounts for the greater fre- 

 quency of stones (calculi) in the bladder and urethra in 

 males. When the bladder becomes filled the mucous 

 membrane comes in contact with the urine, a nervous 

 impulse is sent to the brain and as a consequence the neck 

 (sphincter muscle) of the bladder is relaxed, and the 

 urine is passed, the whole constituting a good illustra- 

 tion of reflex action, the exercise of the will power not 

 being called for. The urine is made use of by chemists 

 and medical men, by the former to estimate the amount 

 of nitrogenous material used or wasted in the body, by 

 the latter to determine the disease, if any, in the person 

 or animal, the operation being known as urinary analysis. 



