432 ABDOMEN 



lateral lobes of the prostate. Bristles should be passed 

 through the apertures into the ducts. 



Owing to the projection of the urethral crest from the 

 middle of the floor of the canal a transverse section of the 

 prostatic portion of the urethra presents a crescentic figure 

 the convexity of the crescent being directed forwards and 

 the concavity backwards. 



The prostate is very liable to become enlarged as old age 

 approaches. When that happens the most important result 

 is the effect exerted on the urethra. If the enlargement is 

 uniform the canal is merely lengthened, but if excessive 

 growth is localised the enlarged part may compress the urethra 

 and interfere with micturition. When the middle lobe enlarges 

 it projects upwards and forwards, over the internal orifice of 

 the urethra, and forms a kind of ball valve, which may 

 prevent the exit of urine through the internal urethral orifice. 

 It is only in pathological conditions that the so-called middle 

 lobe becomes a very distinct and more or less independent 

 part of the organ. During health it is marked off from the 

 rest of the prostate merely by the utricle and by the passage 

 of the ejaculatory ducts through the substance of the 

 gland. 



Pars Membranacea Urethras. The membranous part of 

 the urethra is the narrowest and the shortest division of 

 the urethra. It extends from the prostate to the bulb of the 

 urethra, curving gently downwards and forwards, behind the 

 lower border of the symphysis pubis, from which it is distant 

 about 25 mm. (one inch). Its length is barely three-quarters 

 of an inch ; and the concavity of its curve is directed forwards 

 and upwards. Throughout its entire length it is enveloped 

 by the fibres of the sphincter urethrae membranaceae (O.T. 

 compressor urethras) muscle. Towards its termination the 

 bulbo-urethral glands are placed behind it one on each 

 side. 



The membranous part of the urethra has important rela- 

 tions to the urogenital diaphragm and to the pelvic fascia. 

 As it emerges from the prostate, it pierces the parietal pelvic 

 fascia (i.e. the upper fascia of the urogenital diaphragm), 

 and the margins of the aperture through which it passes are 

 carried backwards to become continuous with the sheath of 

 the prostate. At its termination it pierces the inferior fascia 

 of the urogenital diaphragm, about an inch below the 



