THE URETHRA 1037 



degree. But under the test of catheterism the length of the canal is undoubtedly 

 greater, and may reach seven or eight inches (18-20 cm.) or even more, owing to 

 the traction upon the penis which acconipunies the operation. The canal mav he 

 greatly lengthened also by senile hypertrophy of the prostate, which carries' the 

 internal meatus ui)wards towards the level of tiie top of the symphysis. 



The diameters (^f the passage are scarcely ca))ableof accurati! measurement. In 

 the ordinary condition it is rej>resented by a lissure, and its limits of safe dilata- 

 bility can only be api)roximately "calculated. Otis's investigations show that 

 these limits are wider tlian was formerly believed to be the case, and he has 

 endeavoured to establisli as a law that there is a ratio l^etween the maximum circum- 

 ference of the canal and that of the penis, of four to nine. Thus a penis having 

 in its ordinary state a circumference of thirty-six lines should possess a urethra 

 capable of admitting an instrument of sixteen lines. The sources of fallacy in 

 such an observation are not inconsiderable, but they do not destroy its value as a 

 practical guide to the surgeon. 



The prostatic portion is about an inch and a quarter (3 cm.) in length, wider 

 in the middle than at the two extremities, and almost perpendicular in direction, 

 with a slight inclination downwards and forwards at its lower end. Its anterior 

 wall is concave both in longitudinal and transverse sections, and is studded with 

 the orifices of small mucous follicles; the posterior w^all presents a longitudinal 

 ridge called the colliculus seminalis or verumontanum, highest near the middle 

 and gradually diminishing above and below. A little above the centre of the col- 

 liculus may be seen a rather large opening Avhich leads to a cul-de-sac of especial 

 interest for the morphologist, the sinus pocularis or uterus masculinus, and on 

 the lateral margins of the orifice of the sinus are seen two small ])uucta, one on 

 each side, the openings of the ejaculatory ducts. The sinus pocularis and ducts 

 may be traced upwards and backwards through the prostatic cleft and behind the 

 sphincteric fibres which constitute the prostatic bar or middle lobe of the prostate. 



In consequence of the presence of the colliculus the urethral fissure appears on 

 horizontal section as a U-shaped curve with forward convexity. The recesses cor- 

 responding to the extremities of the U are sometimes called the prostatic sinuses, 

 and into these open the orifices of the posterior and lateral prostatic glands. 



The mucous membrane of the prostatic urethra is lined with a laminated epithe- 

 lium. Beneath this is a layer of erectile tissue which constitutes the princi])al 

 eleuicnt of the colliculus, and is in turn supported by a layer of longitudinal muscle. 



The sinus pocularis is believed to be the homologue of the uterus. It is about 

 half an inch in length, and terminates 1)y a blind, slightly dilated extremity. Its 

 walls consist of connective tissue intermingled with smootli muscular fibres, and 

 covered with laminated epithelium. It contains a few simple or compound glands, 

 in which small concretions are occasionally found. 



The membranous portion, bounded above and below by the superior and 

 inferior triangular ligaments, is about half an inch (12 mm.) in length; it is 

 inclineil downwards and somewhat forwards, and lies aliout an inch (25 nnn.) be- 

 hind the subpubic ligament, from which it is separated l>y the nniscular fibres of 

 the dee]) transversus jK-riuici and a plexus of veins. It is closely related on either 

 side to Cowper's glands. 



The mncovs membrane resembles that of the i)rostatic urethra in its epithelium 

 and erectile layer and muscularis, but surrounding these structures is a strong annu- 

 lar band of unstriped muscle continuous with thefil)res of the prostate and forming 

 a sphincter of considerable power. This in turn is supi)orted by the striated fibres 

 of the deep transversus perinsei. The glands of the mucous mend)rane, simple and 

 racemose, form suite with tiiose of the anterior wall of the prostatic canal. 



The spongy portion extending to the extremity of the penis presents two dila- 

 tations with an intermediate ])ortion of narrow but uniform dimensions. The ]tos- 

 terior expansion ( pars bulbosa i lies in the bulb, and is about an inch (25 nnn.) 

 in length; the anterior (fossa navicularis) is of nearly the same extent, and is 

 situated within the glans. The penile angle, formed wliere the flaccid organ falls 

 from the point of suspension at tlie piiKic region, lies about two inches (5 cm.) in 

 front of the superficial triangular ligament; and the portion of the canal behind this 

 is almost horizontal in direction, but with a slight upward concavity (fig. 617). 



