Chap, xviii.] THE URETHRA. 363 



The urethral canal must not be regarded as 

 forming an open tube like a gas-pipe. Except when 

 urine or an instrument is passing along it, the tube 

 appears on section as a transverse slit, the superior 

 and inferior walls being in contact. This fact should 

 be remembered in amputation of the penis by the 

 ecraseur. In the fossa navicularis the tube appears as 

 a vertical slit. 



The prostatic part of the canal is the widest and 

 most dilatable portion of the whole urethra. It is 

 widest at its centre, having here a diameter of nearly 

 half an inch ; at the bladder end its diameter is about 

 one-third of an inch, while at the anterior extremity of 

 this part of the urethra the measurement is a little less 

 than one-third of an inch. When small catheters are 

 being introduced their points may lodge in the orifice 

 of the utricle, unless the tip of the instrument be 

 kept well along thereof of the canal. The ejaculatory 

 ducts open into the prostatic urethra, and thus it 

 happens that inflammation of this part of the canal 

 may spread back along those ducts to the seminal 

 vesicles, and from thence along the vas deferens to 

 the epididymis. It is by spreading along these parts 

 that inflammation of the testicle is set up in 

 gonorrhoea, involving the prostatic urethra, and it will 

 be understood that a like inflammation may follow 

 lateral lithotomy, impacted stone in the prostatic 

 urethra, prostatic abscess, and the like. Stricture 

 never occurs in this part. 



The membranous urethra is, with the exception 

 of the meatus, the narrowest part of the entire 

 tube. Its diameter is about one-third of an inch. 

 It is fixed between the two layers of the triangular 

 ligament, and is the most muscular part of the canal. 

 It is at this spot, therefore, that what is known as 

 " spasmodic stricture " usually occurs. In any case, 

 the contraction of the compressor urethras often offers 



