URETHRA. 



539 



ference or floor is a longitudinal fold of mucous 

 membrane, the veru montanum, or caput gallina- 

 gmis, and on each side of the veru, a depressed 

 fossa, the prostatic sinus y in which are seen the 

 numerous openings of the prostatic ducts. At the 

 anterior extremity of the veru montanum are the 

 openings of the two ejaculatory ducts, and between 

 them a third opening, which leads backwards into 

 a small caeca! sac, the sinus pocularis. The pros- 

 tatic portion of the urethra, when distended, is the 

 most dilated part of the canal ; but, excepting dur- 

 ing the passage of urine, is completely closed by 

 means of a ring of muscular tissue which encircles 

 the urethra as far as the anterior extremity of the 

 veru montanum. In the contracted state of the 

 urethra, the veru montanum acts as a valve, being 

 pressed upwards against the upper wall of the 

 canal ; but, during the action of the detrusor mus- 

 cle of the bladder, the whole ring is expanded by 

 the longitudinal muscular fibres which are inserted 

 into it ; and the veru is especially drawn down by two delicate tendons, 

 which have been traced by Mr. Tyrrell from the posterior fibres of the 

 detrusor into the tissue of this process. 



The Membranous, portion, the narrowest part of the canal, is somewhat 

 less than an inch in length. It is situated between the two layers of the 

 deep perineal fascia, and is surrounded by the fan-like expansions of the 

 upper and lower segments of the compressor urethrse muscle, which meet 

 at the raphe along its upper and lower surface. It is continuous posteriorly 

 with the prostatic urethra, and anteriorly with the spongy portion of the 

 canal. Its coverings are, the mucous membrane, elastic fibrous layer, 

 compressor urethrse muscle, and a partial sheath from the deep perineal 

 fascia. 



The Spongy portion forms the rest of the extent of the canal, and is 

 lodged in the corpus spongiosum from its commencement at the deep 

 perineal fascia to the meatus urinarius. It is narrowest in the body, and 

 becomes dilated at either extremity, posteriorly in the bulb, where it is 

 named the bulbous portion, and anteriorly in the glans penis, where it 

 forms the fossa navicularis. The meatus urinarius is the most constricted 

 part of the canal ; so that a catheter, which will enter that opening, may 

 be passed freely through the whole extent of a normal urethra. Opening 

 into the bulbous portion are two small excretory ducts about three-quar- 

 ters of an inch in length, which may be traced backwards, between the 

 coats of the urethra and the bulb, to the interval between the two layers 



* The bulbous, membranous, and prostatic urethra, with part of the bladder. 1. Part 

 of the urinary bladder; its internal surface. 2. The trigonum vesicae. 3. The openings 

 of the ureters. 4. The uvula vesicse. 5. The veru montanum. 6. The opening of the 

 sinus pocularis. 7, 7. The apertures of the ejaculatory ducts. 8, 8. The openings of 

 the prostatic ducts. The numbers 7, 7, and 8, 8, are placed on the cut surface of the 

 supra-urethral portion of the prostate gland. 9, 9. The lateral lobes of the prostate gland. 

 a. The membranous portion of the urethra. 6, b. Cowper's glands, c, c. The apertures 

 of the excretory ducts of Cowper's glands, d. The commencement of the bulbous por- 

 tion of the urethra, e, e. The upper surface of the bulb of the corpus spongiosnm. f.f 

 The crura penis, g, g. The corpus cavernosurn. h. The spongy portion of the urethra.' 



