550 A MANUAL OF ANATOMY. 



of an inch behind the lower margin of the symphysis and 

 two inches above the level of the perineum. 



Internal Trig-one. This is the triangular area mapped 

 out by connecting the orifices of the ureters and internal 

 meatus of the urethra by imaginary lines. 



The Urethra. 



This is the membranous tube which forms the outlet to 

 the bladder and seminal vesicles. Its length is approxi- 

 mately six inches when the penis is relaxed. Its diameter 

 to the size of the penis is as four to nine (Otis). 



It is divided into the prostatic portion (one and one- 

 quarter inches long), the membranous portion (one-half 

 to three-fourths of an inch long), and the spongy portion 

 (the remainder of the canal). 



The prostatic portion pierces the prostate from base to 

 apex, lying nearer the anterior than the posterior surface 

 of the gland. 



On section the canal is U-shaped, with the convexity 

 forward and the " legs " backward. 



Within the prostatic portion the following structures are 

 found : 



(i) The verumontanum, or colliculus seminalis. This 

 is a vertical elevation along the posterior wall of the ure- 

 thra, about half an inch long. At its centre is the opening 

 of a blind canal (2), the sinus pocularis, or the uterus mas- 

 culinus. Embryologically related to the female uterus. 

 Below the opening of the sinus pocularis appear (3) the 

 orifices of the ejaculatory ducts, one on each side of the 

 median line. The depressions along the base of the veru- 

 montanum are called (4) the prostatic sinuses, and into 

 them open (5) the ducts of the prostatic glands. 



The membranous portion of the urethra is the only fixed 



