117 



a certain degree of contractility. To the above causes, may be added the 

 concussions excited by the pulsations of the renal arteries, behind which 

 the pelvis of the kidney is situated, and by the pulsations of the iliac ar- 

 teries, in front of which the ureter passes, before entering the cavity of 

 the pelvis ; the alternate compression from the viscera of the abdomen, 

 during the motions of respiration ; the concussion attending bodily exer- 

 cise, as riding on horseback, walking, running, Sec. ; the pressure of the 

 column of urine from the kidneys, and the want of resistance towards the 

 bladder. 



XXXIV. The urine is continually passing, in drops, into the bladder, 

 it separates its parietes, without, however, exciting in them any percepti- 

 ble impression, as they are accustomed to its stimulus. The urine cannot 

 accumulate in the musculo-membranous cavity of the bladder*, which is 

 situated, exterior to the peritoneum, in the cavity of the pelvis, behind the 

 pubis, above which, in the adult, it never rises, except when excessively 

 distended, unless it is prevented from flowing along the urethra, or from 

 returning by the ureters. This retrograde flow is prevented by the ob- 

 lique insertion of these ducts, which pass, for some distance, between the 

 muscular and mucous coats of the bladder, before opening within it, to- 

 wards the posterior angles of the vesicaltrianglef, by openings of smaller 

 dimensions than their cavity. The inner coat of the bladder, raised over 

 these apertures, gives them the appearance of being provided with valves, 

 which fit the better these orifices, according as the urine contained in the 

 bladder, by separating its parietes, presses against each other the coats 

 by which they are formed, and between which the ureters pass, along a 

 space of from seven to eight lines. 



The urine which flows into the bladder, requires a certain degree of 

 force, to separate its parietes on which the weight of the intestines press- 

 es. This is effected by no other power, than by that which causes the 

 flow of the urine along the ureters, and though inconsiderable, it will ap- 

 pear sufficient, if it be considered that the fluids which pass from a strait 

 channel into a larger cavity, act on every superficial portion of its parietes 

 equal to the area of the channel, with a power equal to that which deter- 

 mines their flow into the latter; so that if the urine descends along the 

 ureters, with a degree of force equal to one, and if the inner surface of 

 the bladder is a thousand times more extensive than the area of the ure- 

 ters, the power will be multiplied a thousand fold. 



This purely mathematical proposition is expressed by saying, that the 



* In the numerous tribe of birds, the bjfedder is wanting. In them, the ureters open 

 into the cloaca, a musculo-membranous bag, which supplies the place of the rectum, 

 bladder, and uterus, and which serves as a reservoir to the solid excrements, to the 

 urine, and to the eggs detached from the ovaria. The urine of birds dilutes the faces, 

 and furnishes the carbonate of lime which forms the basis of the egg-shell. It has such 

 a tendency to concretion, that 1 have always observed, in dissecting various fowls of 

 different kinds, an earthy, saline, or crystallized substance, forming white striae easily 

 seen in the fluid of the ureters, through their skin and transparent coats. Hence one 

 may readily conceive, how frequently calculi would form in these animals, if their 

 urine accumulated and remained, for any length of time, stationary in a cavity destined 

 to contain it Jluthor's Note. 



| The French anatomists give the name of trigone -vesicae, to that portion of the 

 bladder, included between the openings of the ureters and the neck of the bladder, 

 and forming a triangle, whose base is represented by a line drawn from the opening of 

 one ureter to the other, and whose apex is situated at the insertion of the urethra into 

 the neck of the bladder. Translator. 



