428 THE URINARY APPARATUS. 



Ureters. From each kidney passes a ureter, a tube which 

 connects the kidney with the bladder, and through which the 

 urine is discharged. It has a diameter about that of a goose-quill 

 and a length of about 40.6 cm. It has 3 coats : External or 

 fibrous; middle or muscular; and internal or mucous. The 

 muscular tissue is of the plain variety and arranged in 2 layers : 

 longitudinal and circular ; a third layer, also longitudinal, is found 

 near the bladder. The mucous membrane is covered with transi- 

 tional epithelium (p. 34). 



When the ureters reach the base of the bladder, they pass for 

 about 2 cm. between the muscular and mucous coats, and then 

 open by a constricted orifice in the bladder. 



Function of the Ureters. The urine which is being constantly 

 formed by the kidneys passes into their pelves, and by peristaltic 

 action of the muscular coat of the ureters is carried to the bladder, 

 into which it flows intermittently. The actual entrance of the 

 urine has been observed in a case of ectopia vesicce in a boy. This 

 condition consists in a deficiency in the abdominal wall and in 

 the front wall of the bladder, so that the openings of the ureters 



FIG. 243. Casper's ureter cystoscope : li, movable lid covering groove in which 

 moves c, the ureteral catheter ; d, handle of lid ; o, ocular end ; p, prism ; I, lamp, 

 s, screw for makipg and breaking connection with the battery ; m, mandril. 



can be inspected. In this case the flow of urine into the blad- 

 der was intermittent, and about the same in amount for each 

 ureter. 



By means of the cystoscope (Fig. 243) it has been determined 

 that the peristaltic action of the ureters is both intermittent and 

 alternate ; exceptionally it may be synchronous. At intervals 

 of a minute or more urine is discharged from the ureters into the 

 bladder, the amount varying; but averaging, perhaps, from 1.5 to 

 30 drops. 



The cause of this peristaltic contraction is not definitely deter- 

 mined. Some authorities attribute it to the direct stimulation of 

 the muscular tissue by the accumulated urine, which results in a 

 wave which is propagated from one muscle-cell to another ; while 

 others think that this contractility of the musculature of the 

 ureters is a power possessed by it independent of any direct stim- 

 ulation, either mechanical or nervous. Experiments upon the rat 

 have demonstrated that when the ureter is cut into several pieces, 

 each section will contract peristaltically. 



