chap, xviii.] THE URETHRA. 403 



part extends from the neck of the bladder to the 

 posterior extremity of the penile urethra at the point 

 of attachment of the suspensory ligament. The fixed 

 part describes an even curve, fairly represented by 

 the line of a " short curve " metal catheter. The 

 two ends of the curve lie about in the same line, 

 viz, one drawn across the lower end of the sym- 

 physis, and at right angles to the vertical axis of 

 that articulation. The curve is formed around this 

 line, its summit corresponding to a prolongation of 

 the vertical axis of the symphysis, and to about the 

 centre of the membranous urethra. This part of 

 the tube lies about one inch below the pubic arch. 

 The movable portion of the urethra forms, when the 

 penis is dependent, a second curve in the opposite 

 direction, so that the whole canal follows somewhat 

 the outline of the letter S. 



The prostatic portion of the urethra will be nearly 

 vertical. This part of the canal corresponds to the pos- 

 terior ventral part of the urogenital sinus of the cloaca, 

 which receives the Wolffian and Miillerian ducts. The 

 prostatic sinus in this part of the urethra represents the 

 united ends of the rudimentary Miillerian ducts. 



That part of the urethral canal which lies beyond the 

 prostate is of different origin, and is a portion of the 

 anterior segment of the cloaca, which has been formed 

 into a canal by a superficial union of the tegumentary 

 folds in the median line. 



The penile or spongy portion of the urethra is sur- 

 rounded by the erectile tissue of the corpus spongiosum 

 urethrae, which is thickest on the under side of the canal. 

 A very thin layer of erectile tissue surrounds the mem- 

 branous urethra lying beneath the fibres of the com- 

 pressor urethrae. 



In introducing a catheter it must be noted that 

 while the instrument parses along the movable 

 urethra, the canal accommodates itself to the catheter, 



