1264 UROGENITAL SYSTEM 



tion are the minute openings of the numerous ducts of the prostate gland 

 (fig. 1025). 



On its emergence from the prostate gland the urethra at once penetrates the 

 deep layer of fascia of the urogenital trigone and enters the deep perineal inter- 

 space, this portion of its course being known as the membranous portion [pars 

 membranacea]. Its direction is now downward and slightly forward, curving 

 beneath the subpubic hgament, from which it is separated by a plexus of veins and 

 by the fibres of the sphincter urethrse membranacese, which form an almost 

 complete investment for it. The lumen of this part of the urethra is much 

 narrower than that of the prostatic portion, and since it traverses the rather 

 unyielding fasciae of the urogenital trigone it is less dilatable than in other parts 

 of its extent, with the exception of the external orifice. 



Passing through the superficial layer of fascia of the urogenital trigone the 

 urethra then enters the bulb of the corpus cavernosum urethrse (fig. 1024) and is 

 invested throughout the remainder of its extent by this structure, whence this 

 portion is known as the cavernous portion [pars cavernosa]. In its proximal part 

 this lies in the superficial interspace of the perineum and passes almost directly 

 forward; but more distally, where it enters the body of the penis, it accommodates 

 itself to the position of that organ, which it traverses lengthwise, lying in the mid- 

 line near its ventral surface (fig. 1022). Thus the proximal portion of the 

 cavernous and the whole of the membranous and prostatic portions have a 

 fixed position, whence they are sometimes associated as the pars fixa of the urethra, 

 while the penial portion forms the pars mohilis. On entering the bulb the lumen 

 of the urethra dilates somewhat and in this region has opening into it the ducts of 

 the bulbo-urethral glands (fig. 1025), but as it enters the body of the corpus caver- 

 nosum it diminishes again and maintains a uniform diameter throughout the 

 extent of that structure. When it reaches the glans penis it undergoes another 

 dilation, which is known as the fossa navicularis (fig. 1025), beyond which it 

 diminishes to the slit-like external orifice, situated at the extremity of the glans 

 and forming the least dilatable portion of the entire urethral canal. 



Throughout the greater part of its extent the cavernous portion of the urethra shows upon 

 its dorsal wall the openings of numerous tubular depressions of the mucous membrane, the 

 urethral lacunce [lacunae urethrales (Morgagnii)]. One of these, the lacuna magna, situated 

 in the mid-dorsal line of the proximal part of the fossa navicularis, has its orifice guarded by a 

 valve-like fold [valvula fossae navicularis] of the mucous membrane and is sufficiently large to 

 receive the point of a small catheter. Numerous minute glands [gl. urethrales] open upon 

 the surface of the urethral mucosa. They are most abundant in the anterior wall, but occur 

 also on the sides and floor. 



Dimensions of the urethra. — The entire length of the urethra is somewhat variable in 

 different individuals, the greatest variation being in the length of the pars mobilis. Of the pars 

 fixa the prostatic portion is 2.5-3.0 cm. in length, the membranous portion about 1.0 cm., and 

 the fixed part of the cavernous portion 6.5 cm., the entire pars fixa having thus a length of some- 

 what over 10.0 cm. (4 in.). The average diameter of the urethra is 5.0-7.0 mm., but it will be 

 noted that the canal presents in its course three dilatations; namely, (1) at the fossa navic- 

 ularis, which begins about 0.5 cm. from the external orifice; (2) the bulb of the corpus caverno- 

 sum urethrie; and (3) in the prostatic portion. Furthermore there are two regions in which it 

 is distinctly narrowed; namely, at the external orifice and in the membranous portion. While 

 the remaining portions are capable of considerable distention, these are relatively indistensible, 

 the maximum diameter to which they may be dilated being about 10 mm. Arranged in an 

 a.scending order according to their capability for distention the parts would have the following 

 order: external orifice, membranous portion, penial portion, prostatic portion, bulbar portion. 



5. The Prostate Gland 



^riio prostate gland [prostata] (figs. 1013, 1019, 1024 and 1025) is a mass of 

 glandular and muscular tissue surrounding the proximal portion of the male 

 urethra, and may, indeed, be regarded as a special development of the wall of 

 this portion of the canal. It is a more or loss flattened conical structure whose 

 base [basis prostatic] is in contact with the lower surface of the bladder and the 

 apex [apex prostatic] with the deep fascia of tiie urog(niital trigone. Its anterior 

 surface [fades anterior] is in relation with tlic sympliysis pubis, from which it is 

 separated l)y the pudendal plexus of veins, and posteriorly [facies ])osterior] it is 

 scjparated from the lower portion of the rectum only by some loose connective 

 tissue; laterally it is in relation with the levatores ani, receiving an investment from 

 the endopcilvic fascia covering these. 



