404 SURGICAL APPLIED ANATOMY. [Chap. xvm. 



but while traversing the fixed segment the instrument 

 must accommodate itself to the unyielding canal. In 

 introducing a catheter in the recumbent posture the 

 penis is held vertically upwards, and in this way the 

 curve formed by the movable urethra is obliterated. 

 The instrument is best kept close to the surface of the 

 groin, and over and pai'allel to Poupart's ligament. 

 When the fixed urethra is reached, the handle of the 

 catheter is brought to the middle line, and then, being 

 kept strictly in the median plane of the body, is 

 depressed between the legs, so that the front of the 

 instrument may follow the natural curve of the 

 canal. The greatest difficulty in the introduction is 

 generally experienced at the point where the movable 

 and fixed parts of the urethra meet ; or, rather, in 

 practice, at a spot a little behind this point, viz. at 

 the anterior layer of the triangular ligament. At this 

 spot the tube becomes abruptly, not only very fixed, 

 but also very narrow, and a part of it is reached 

 where muscular tissue is very abundant, and where 

 resistance from muscular spasm is therefore likely to 

 be most marked. 



It thus happens that when a false passage has 

 been made by a catheter in a case where no stricture 

 exists to offer a definite obstruction, the instrument 

 is usually found to have left the canal just in front of 

 the triangular ligament. 



Some other points in connection with catheterism 

 will be noted subsequently. 



The urethra! casial 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. 



