URETHRA AND BLADDER. 



537 



ejaculatory ducts, and between them a third opening, which leads 

 backwards into a small dilated sac the sinus pocularis. The pro- 

 static portion of the urethra, when distended, is the most dilated part 

 of the canal ; but, excepting during the passage of urine, is com- 

 pletely closed by means of a ring of elastic tissue which encircles 

 the urethra as far as the anterior extremity of the verumontanum. 

 In the contracted state of the urethra, the verumontanum acts as 

 a valve, being pressed upwards against the upper wall of the canal ; 

 but, during the action of the detrusor muscle of the bladder, the 

 whole elastic ring is expanded by the muscular fibres which are 

 inserted into it ; and the veru is especially drawn downwards by 

 two delicate tendons, which have been traced by Mr. Tyrrell, 

 from the posterior fibres of the detrusor into the tissue of this 

 process. 



Fig. 160* 



* A longitudinal section of the bladder, prostate gland, and penis, showing the 

 urethra. 1. The urachus attached to the upper part of the fundus of the bladder. 2. 

 The recto-vesical fold of peritoneum, at its point of reflection from the base of the 

 bladder, upon the anterior surface of the rectum. 3. The opening of the right ureter. 

 4. A slight ridge, formed by the muscle of the ureter, and extending from the termi- 

 nation of the ureter to the commencement of the urethra. This ridge forms the lateral 

 boundary of the trigonum vesicce. 5. The commencement of the urethra ; the eleva- 

 tion of mucous membrane immediately behind the figure is the uvula vesicae. The 

 constriction of the bladder at this point is the neck of the bladder. 6. The prostatic 

 portion of the urethra. 7. The prostate gland ; the difference of thickness of the 

 gland, above and below the urethra, is shown. 8. The isthmus, or third lobe of the 

 prostate ; immediately beneath which the ejaculatory duct is seen passing. 9. The 

 right vesicula seminalis ; the vas deferens is seen to be cut short off, close to its junc- 

 tion with the ejaculatory duct. 10. The membranous portion of the urethra. 11. 

 Cowper's gland of the right side, with its duct. 12. The bulbous portion of the 

 urethra ; throughout the whole length of the urethra of the corpus spongiosum, nu- 

 merous lacunae are seen. 13. The fossa navicularis. 14. The corpus cavernosum, cut 

 somewhat obliquely to the right side, near its lower part. The character of the venous- 

 cellular texture is well shown. 15. The right crus penis. 16. Near the upper part of 

 the corpus cavernosum, the section has fallen a little to the left of the middle line ; a 

 portion of the septum pcctiniformc is consequently seen. This figure also indicates 

 the thickness of the fibrous investment of the corpus cavernosum, and its abrupt ter- 

 mination at the base of (17) the glans penis. 18. The lower segment of the glans. 

 19. The meatus urinarius. 20. The corpus spongiosum. 21. The bulb of the corpus 

 spongiosum. 



68 



