472 URO-GEN1TAL SYSTEM. 



of urine and urea much below the standard of health. Vul- 

 pian determined more precisely the modification of the uri- 

 nary secretion by the sympathetic branches ; his experiments 

 were made on the splanchnic nerves. As soon as either of 

 the splanchnic nerves was cut, the corresponding kidney was 

 injected, reddened, and increased in size ; the vein distended, 

 and the blood assumed an arterial brightness; finally, the 

 urine secreted contained a much greater amount of albu- 

 men. 1 



C. Excretion of urine. 



The pressure which causes a filtration of urine pushes it 

 along through the uriniferous tubes, and produces a sort of 

 vis a tergo, which sends the liquid as far as the summit of 

 the pyramids (papillae renales, papilla of the kidney), 

 whence it flows out of numerous little pits, the papillary 

 orifices, into the calyces of the pelvis; this same force, 

 vis a tergo, is continually exerted through the course of the 

 ureters as far as the bladder, for it is hardly probable that the 

 contraction of their muscular walls is called in play to assist 

 by a series of waves the propulsion of the urine ; in fact, in 

 cases of extroversion of the bladder in which the ureters 

 open in front of the lower portion of the abdomen, as it were, 

 in open sight, the urine may be seen flowing drop by drop 

 through these orifices only as it is produced, and in no wise 

 is propelled by jerks as would be the consequence of muscu- 

 lar contractions. The ureters open into the bladder by 

 traversing in an oblique direction the walls of this reservoir ; 

 when the bladder is very much distended the pressure on 

 these orifices must be quite considerable, and the delivery of 

 a fresh amount of liquid be greatly impeded. At such times 

 the contractility of the ureters will assist by propelling the 

 urine with a peristaltic movement, which will afford sufficient 

 force to overcome the resistance to the passage of urine 

 along the vesical walls. 



The bladder is a reservoir resulting from the dilatation of 

 the urachus or attantoid pedicle of the foetus. Its interior is 

 lined by an epithelium, outside of which are more or less 

 regular muscular layers. 



The vesical epithelium is of the pavement or stratified 

 form, but its superficial cellular elements are remarkable for 

 their irregularity and oddity of shape (Fig. 128). From the 



11 Vulpian, " Societe de Biologic." Mai, 1873. 



