STEICTUEE OF THE UEETHEA. 437 



of the membranous part of the tube. Only mucous glands 

 open into this latter part of the urethra. 



The prostatic portion is wide, and on its floor is found an 

 elevation, on the summit of which there opens the sinus pocu- 

 laris, and on each of its sides the common ejaculatory duct. 

 The urethra terminates in the bladder at a spot which, in the 

 adult, is one inch behind the upper border of the symphysis 

 pubis, and three inches from the skin surface of the perineum. 

 The urethra is partially covered with voluntary muscles, the 

 bulbo-cavernosus around the bulbous part, and the constrictor 

 urethrsB (deep transversus perinei) about the membranous 

 portion. 



The passage of a catheter or other instrument along the healthy 

 urethral channel may be obstructed first by the narrowness of 

 the external meatus, and then by the actual curvature of the 

 tube. Thus it becomes desirable to draw up the penis over 

 the symphysis in the early stage of passing a catheter, so as to 

 convert the double curve of the passage into a single long one. 

 During its passage the tip of a catheter may lodge in the 

 lacuna magna, or against a possible fold of mucous membrane, 

 caught up as it were by the instrument. Its progress also may 

 be impeded by the spasmodic contraction of the peri-urethral 

 muscles. Frequently the point of the catheter may be run 

 against the superficial layer of the triangular ligament, not 

 properly engaging the entrance into the membranous portion of 

 the urethra. Beyond this spot there is little to interfere with 

 the onward passage of the instrument in the normal tube. 

 When, however, there is an enlargement of the prostate, 

 particularly when a so-called middle lobe is hypertrophied, 

 much obstruction at the entrance into the bladder may be 

 met with. 



Organic stricture of the urethra is most common at the junc- 

 tion of the bulbous with the membranous portion of the urethra, 

 and this is accounted for by the fact that the urethra passes 

 through the anterior layer of the triangular ligament at this spot, 

 that annular ulcers of gonorrhoeal origin are most frequently 



