THE PELVIS 365 



pierces its base, traverses its substance, and emerges a little 

 above its apex. It is also pierced by the common ejaculatory 

 ducts (p. 367). 



A well-marked groove separates the prostate from the 

 bladder externally. At this level the prostatic sheath contains 

 in its walls the pudendal (prostatico-vesical) plexus of veins, which 

 receives the dorsal vein of the penis (p. 386), and tributaries 

 from the bladder and prostate. The prostatic veins cross the 

 potential interval between the capsule and the sheath to reach 

 the plexus, and are consequently torn in prostatectomy. 

 (Compare this arrangement with the course of the thyreoid 

 veins, p. 168.) 



The pudendal plexus terminates in the large veins which 

 have already been mentioned in connection with the posterior 

 pedicle of the bladder (p. 362). 



Hypertrophy of the Prostate usually involves the glandular 

 tissue, and may be confined to the " middle lobe " ; but the whole 

 prostate may become enlarged. The dense, unyielding character 

 of the sheath limits the growth in antero-posterior and lateral 

 directions, but the neck of the bladder offers little resistance 

 to upward extension. As a result the prostatic tissue projects 

 into the bladder through the internal sphincter and forms a 

 collar-like elevation around the internal urethral orifice. The 

 muscular tissue which connects the prostate and the bladder is 

 stretched and thinned out, so that few or no fibres are encountered 

 by the surgeon in prostatectomy (p. 366), and the tumour is 

 exposed as soon as the mucous membrane over it has been torn 

 through. 



Owing to the direction of growth the prostatic urethra 

 becomes increased in length from ij to 2 or 2^ inches, and at 

 the same time its forward concavity becomes proportionately 

 greater. 



The so-called " middle lobe " of the prostate is that part 

 which intervenes between the ejaculatory ducts (p. 367) and 

 the urethra. Its upper surface lies under the mucous coat 

 of the tiigone of the bladder, immediately behind the internal 

 urethral orifice, and when well marked produces a slight elevation 

 known as the uvula vesicce. When hypertrophy affects the 

 middle lobe only, the prostate is apparently normal on rectal 

 examination. In these cases the enlarged uvula seriously 

 hinders the escape of urine through the internal urethral orifice 

 and constitutes one of the worst forms of urinary obstruction. 



