520 EVACUATION OF THE URINE. 



downward to the middle of the urethra and lie next to the unstriated cir- 

 cular fibers, and in part of longitudinal fibers, which pass upward to the 

 base of the bladder only on the posterior wall of the urethra, and down- 

 ward between the circular fibers. Additional circular fibers are situated 

 below the middle of the urethra, and only in isolated distribution on its 

 anterior surface. 



In the male urethra, the epithelium of the prostatic portion still resembles 

 that of the bladder, in the membranous portion it becomes laminated, and in 

 the cavernous portion a simple cylindrical epithelium. The mucous membrane 

 beneath the laminated epithelium, provided with papillae, contains, principally in 

 the posterior portion, the mucus-secreting glands of Littre. Unstriated muscle- 

 fibers are present in the prostatic portion as a longitudinal layer, especially at 

 the colliculus seminalis; while the membranous portion contains principally cir- 

 cular fibers, with intervening longitudinal fibers. The cavernous portion contains 

 posteriorly delicate circular fibers, anteriorly only isolated insignificant oblique 

 and longitudinal fibers. 



With respect to the mechanism for closure of the male urethra, it 

 should be pointed out that the so-called internal sphincter vesicse of the 

 anatomists, which consists of unstriated muscular fibers, and, as an integ- 

 ral portion of the musculature of the bladder surrounds the commencement 

 of the urethra down to within the prostatic portion of the urethra, 

 above the colliculus seminalis, is not a sphincter muscle at all. The true 

 striated sphincter of the urethra, or external sphincter of the bladder, is 

 situated below the former. It is a completely circular muscle, surround- 

 ing the urethra, just above the entrance of the urethra into the urogen- 

 ital septum, at the apex of the prostate gland, where its fibers anasto- 

 mose with those of the subjacent deep transverse peroneal muscle. 



This sphincter muscle includes, also, longitudinal fibers, which pass downward 

 from the bladder along the upper border of the prostate. Isolated transverse 

 bundles are derived anteriorly from the surface of the neck of the bladder. 

 The sphincter muscle includes, besides, certain transverse fibers that lie within 

 the prostate even opposite the apex of the colliculus seminalis, passing like a 

 thick transverse column in advance of the commencement of the urethra into the 

 structure of the prostate prostatic muscle. 



In the male urethra, the blood-vessels form a rich capillary network beneath 

 the epithelium, in the midst of which a wide-meshed lymphatic vascular net- 

 work is situated. 



COLLECTION AND RETENTION OF THE URINE IN THE BLADDER. 

 EVACUATION OF THE URINE. 



After the evacuation of the bladder, urine reaccumulates, with grad- 

 ual distention of the viscus. As long as the amount of urine is but mod- 

 erate, the elasticity of the elastic fibers surrounding the urethra and of 

 the sphincter muscle of the urethra in men, in addition, that of the 

 prostate suffices perfectly to retain the urine in the bladder. This is 

 indicated by the fact that in the cadaver the urine does not escape from 

 the bladder. The movements for the evacuation of the bladder, as 

 well as for the retention of the urine in the bladder, exhibit, in many 

 respects, an agreement with the motor mechanism at the rectum. In 

 the first place, it should be pointed out that the walls of the bladder are 

 capable of independent contraction. Whether these are due to the 

 ganglion-cells in the bladder that are found in the course of the nerves 

 has not been demonstrated. It is rather more likely that the muscula- 

 ture of the bladder is capable of rhythmic movement without nervous aid. 



