URETHRA. 



527 



and downwards in the prostate, for a quarter of an inch, passing beneath 

 the middle and between the lateral lobes. Its orifice in the urethra is 

 about a line wide, and its closed extremity is about as large again. Along 

 the wall, on each side, is placed the common seminal duct (/), which ter- 

 minates on or within the margin of the mouth of the sac ; and if bristles 

 are introduced into the common seminal duct behind the prostate, they 

 will render evident the apertures. Small glands open on the surface of the 

 mucous membrane lining the utricle. The vesicula is the remains of the 

 united lower ends of the ducts of Miiller in the foetus, and represents the 

 uterus in the female. 



Fig. 180. 



a. Bladder. 



b. Prostate, and c, prostatic part of the 



urethra. 



d. Vesicula seminalis. 



e. Vas deferens. 



/. Common ejaculatory duct. 

 g. Vesicula prostatica. 



SECTION THROUGH THE BLADDRR, PROSTATE, AND URKTHRA, to show the vesicula prostatica 

 and the common seminal duct. 



On each side of the central crest is an excavation, which is named the 

 prostatic sinus (fig. 181, /). Into this hollow the greater number of the 

 ducts in the prostate open ; but the apertures of some are seen at the 

 posterior part of the central eminence. 



The membranous part of the urethra (fig. 181, g) is three-quarters of 

 an inch in length, and intervenes between the apex of the prostate gland 

 and the bulb () of the corpus spongiosum urethrse. In its interior are 

 slight longitudinal folds. This is the narrowest portion of the whole tube, 

 with the exception of the outer orifice, and measures rather less than a 

 quarter of an inch across. It is the weakest of the three portions of the 

 canal, and is supported by a thin stratum of erectile tissue, by a thin layer 

 of unstriated circular fibres (p. 397), and outside all by the constrictor 

 urethras muscle. 



The spongy part (fig. 181, i) reaches to the end of the penis. It is 

 about six inches in length. And its strength depends upon a surrounding 

 material named corpus spongiosum urethras. 



The average size of the canal is about a quarter of an inch in diameter, 

 though at the vertical slit (meatus urinarius), by which it terminates on 

 the glans penis, the tube is smaller than elsewhere. On a cross section it 

 appears as a transverse slit, but in the glans, as a vertical interval. Two 

 dilatations exist in the floor of the spongy portion : One is close to the 

 triangular ligament, being contained in the bulb or bulbous part of the 



