364 SURGICAL APPLIED ANATOMY. [Chap. xvm. 



an appreciable amount of resistance to the passage of 

 a catheter or sound. 



The penile urethra is dilated at either end ; 

 viz., at the parts occupying the bulb and the glans 

 penis respectively. The diameter of the bulbous 

 urethra is midway between that of the prostatic and 

 membranous segments of the canal, while that of 

 the greater part of the penile urethra is midway 

 between that of the bulbous and membranous portions. 

 It is in the bulbous urethra that organic stricture is 

 the most commonly met with. The meatus measures 

 from one-fifth to one-fourth of an inch, and therefore 

 if a catheter will pass the meatus it will pass along 

 any part of the canal if normal. Its aperture is very 

 resisting, and has often to be incised to allow the 

 larger instruments to pass. 



The narrowest parts of the urethra, therefore, are 

 at (1) the meatus, and (2) in the membranous segment, 

 especially at its anterior end. It is at these points 

 that calculi passed from the bladder are most apt to 

 lodge. The widest portions of the canal, on the other 

 hand, are at (1) the fossa navicularis, (2) the bulbous 

 part of the urethra, and (3) the centre of the prostatic 

 portion. 



The mucous membrane presents, in addition 

 to many mucous glands, several lacunae, the orifices of 

 which for the most part open towards the meatus. 

 These lacunae are most numerous in the bulbous 

 urethra, and occupy the floor rather than the roof of 

 the canal. In passing small catheters, therefore, the 

 point of the instrument should be kept along the 

 upper surface of the tube, so that it may not become 

 engaged in any of these spaces. The largest lacuna, 

 the lacuna magna, is situate in the roof of the fossa 

 navicularis, and may readily engage the point of a 

 small instrument. 



Otis has endeavoured to show that a definite 



