THE URETHRA. 



1925 



FIG. 



Surface epithelium 



Crypts 



the orifices of the ducts of Cowper's glands. The circular fibres, outside the longitudi- 



nal, are best developed at the internal orifice, where they form a layer three or four 



times as thick as the longitudinal, which they accompany as a distinct, although di- 



minishing, stratum as far 



forward as the termination 



of the membranous ure- 



thra, disappearing first on 



the lower and last on the 



upper wall of the fossa 



bulbi. Beyond the pos- 



terior third of the pars 



spongiosa the intrinsic 



muscle is wanting, the 



muscular tissue surround- 



ing the remaining parts 



belonging to the erectile 



tissue of the corpus spon- 



giosum (Zuckerkandl). 



The internal vesical 

 sphincter encircling the 

 commencement of the ure- 

 thra is derived from the 

 deeper layer of the mus- 



----- * 



-;. - 



Section of mucous membrane of prostatic urethra, showing 

 gland-like crypts in mucosa. X 45- 



Surface epithelium 



cular sheet of the trigone ; 



the muscle of the adjacent vesical wall does not directly take part in its production 



(Kalischer). 



At the apex of the prostate the urethra is encircled by bundles of striped muscle 

 known as the external vesical sphincter. Higher up these bundles lie entirely in 

 front of the urethra in close relation with the lower border of the involuntary sphincter, 

 in front of which they extend. Below, the external sphincter is continuous with the 

 compressor urethrae muscle, as an upward prolongation of which it may be regarded 

 (Holl). As it passes between the two layers of the triangular ligament, the mem- 

 branous portion of the 



FIG. 1634. urethra is enclosed by 



stout annular bundles of 

 the compressor urethrae 

 muscle, which when stim- 

 ulated to contraction, as 

 by the presence of an in- 

 strument in the canal, 

 may tightly embrace the 

 urethra and embarrass 

 the passage of the cathe- 

 ter. These fibres are 

 continued forward for 

 some distance beyond the 

 lower layer of the trian- 

 gular, ligament. 



Since they affect the 

 canal, although not in 

 intimate relation with its 

 wall, the fibres of the 

 bulbo-cavernosus muscle 

 may also be included in 

 the extrinsic urethral 

 musculature. 



Blood-vessels 

 in mucosa 



Venous spaces 

 of cavernous 

 tissue 



Section of wall of urethra in spongy portion, showing crypts 

 in mucosa and numerous venous spaces. X 35- 



The urethral glands, 



or glands of LtOre, embrace two groups those within the mucous membrane and 

 those within the submucous tissue the ducts of which are seen with a magnifying- 



