136 DISEASES OF THE HORSE. 
ternal (medullary) part, made up in the main of blood vessels, 
lymphatics, and nerves extending between the notch on the inner 
border of the kidney to and from the outer vascular portion, in which 
the secretion of urine is almost exclusively carried on; and (d) a 
large, saccular reservoir in the center of the kidney, into which all 
uriniferous tubes pour their secretions and from which the urine 
is carried away through a tube g (ureter), which passes out of the 
notch at the inner border of the kidney and which opens by a valve- 
closed orifice into the roof of the bladder just in front of its neck. 
The bladder is a dilatable reservoir for the retention of the urine 
until the discomfort of its presence causes its voluntary discharge. 
It is kept closed by circular, muscular fibers surrounding its neck 
or orifice, and is emptied by looped, muscular fibers extending in 
all directions forward from the neck around the blind anterior end 
of the sac. From the bladder the urine escapes through a dilatable 
tube (urethra) which extends from the neck of the bladder backward 
on the floor of the pelvis, and in the male through the penis to its 
free end, where it opens through a pink, conical papilla. In the mare 
the uretha is not more than an inch in length, and is surrounded by 
the circular, muscular fibers closing the neck of the bladder. Its 
opening may be found directly in the median line of the floor of the 
vulva, about 44 inches from its external opening. 
GENERAL SYMPTOMS OF DISEASE. 
These apply especially to acute inflammations and the irritation 
caused by stone. The animal moves stiffly on the hind limbs, strad- 
dles, and makes frequent attempts to pass urine, which may be in 
excess, deficient in amount, liable to sudden arrest in spite of the 
straining, passed in driblets, or entirely suppressed. Again, it may 
be modified in density or constituents. Difficulty in making a sharp 
turn, or in lying down and rising with or without groaning, drop- 
ping the back when mounted or when pinched on the loins is sugges- 
tive of kidney disease, and so to a less extent are swelled legs, dropsy, 
and diseases of the skin and nervous system. The oiled hand intro- 
duced through the rectum may feel the bladder beneath and detect 
any overdistention, swelling, tenderness, or stone. In ponies the kid- 
neys even may be reached. 
EXAMINATION OF THE URINE. 
In some cases the changes in the urine are the sole sign of disease. 
In health the horse’s urine is of a deep amber color and has a strong 
odor. On a feed of grain and hay it may show a uniform transpar- 
ency, while on a green ration there in an abundant white deposit of 
carbonate of lime. Of its morbid changes the following are to be 
