DISEASES OF THE URINARY ORGANS. 141 



Deeply covered in a mass of suet, each kidney has a strong outer white, 

 fibrous covering, and inside this two successive layers of kidney sub- 

 stance, of which the outer is that in which the urine is mainly separated 

 from the blood and poured into the fine microscopic urinary ducts. 

 ( Plate x, Fig. 1. ) These latter, together with blood vessels, lymph vessels, 

 and nerves, make up the second or internal layer. The outer layer is 

 mainly composed of minute globular clusters of microscopic intercom- 

 municating blood-vessels (Malphigian bodies), each of which is furnished 

 with a fibrous capsule that is nothing else than the dilated commence- 

 ment of a urine tube. These practically microscopic tubes follow at first 

 a winding course through the outer layer (Ferrein's tubes), then form a 

 long loop (doubling on itself) in the inner layer (Henle's loop), and finally 

 pass back through the inner layer (Bellini's tubes) to open through a 

 conical process into the common pouch (pelvis) on the lower surface of 

 the organ. (Plate x, Figs. 1, 2, 3). 



The tube that conveys the urine from the kidney to the bladder is like 

 a white round cord about the size of a goose-quill, prolonged from the 

 pouch on the lower surface of the kidney backward beneath the loins, 

 then inward, supported by a fold of thin membrane, to open into the 

 bladder just in front of its neck. The canal passes first through the 

 middle (muscular) coat of the bladder, and then advances perceptibly 

 between that and the internal coat (mucus), through which it finally 

 opens. By this arrangement in overfilling of the bladder this opening 

 is closed like a valve by the pressure of the urine, and the return of 

 liquid to the kidney is prevented. The bladder (Plate ix, Fig. 2) is a 

 dilatable egg-shaped pouch, closed behind by a strong ring of muscular 

 fibers encircling its neck, and enveloped by looped muscular fibers ex- 

 tending on all sides round its body and closed anterior end. Stimu- 

 lated by the presence of urine, these last contract and expel the con- 

 tents through the neck into the urethra. This last is the tube leading 

 backward along the floor of the pelvic bones and downward through 

 the penis. In the bull this canal of the urethra is remarkable for its 

 small caliber and for the S-shaped bend which it describes in the inter- 

 val between the thighs and just above the scrotum. This bend is due 

 to the fact that the retractor muscles are attached to the penis at this 

 point, and in withdrawing that organ within its sheath they double it 

 upon itself. The small size, of the canal and this S-shaped bend are 

 serious obstacles to the passing of a catheter to draw oft' the urine, yet 

 by extending the penis out of its sheath the bend is effaced, and a small 

 gum-elastic catheter, not over one-quarter of an inch in diameter, may 

 with care be passed into the bladder. In the cow the urethra is very 

 short, opening in the median line on the floor of the vulva about four 

 inches in front of its external orifice. Even in the cow, however, the 

 passing of a catheter is a matter of no little difticulty, the opening of 

 the uretha being very narrow and encircled by their projecting mem- 

 branous and ritfiu mar-ins, and on each side of the opening is a blind 



