MUCOUS MEMBRANE. 439 



sum. It measures three quarters of an inch aiong its anterior, but 

 only about half an inch on its posterior surface, in consequence of the 

 projection backwards on it of the bulb. This is the narrowest division 

 of the urethra. In the middle its circumference is 0'6 of an inch : at 

 the end 0'5. It is placed beneath the pubic arch, the anterior con- 

 cave surface being- distant nearly an inch from the bone, leaving an 

 interval, occupied by the dorsal vessels and nerves of the penis, by 

 areolar tissue, and some muscular fibres. Its lower convex surface 

 is turned towards the periuEcum, opposite to the point of meeting 

 of the transverse muscles : it is separated by an interval from the 

 last part of the rectum. About a line in front of the prostate, it 

 emerges from between the anterior borders of the levatores ani, and 

 passes through the deep laj'er of the subpubic fascia ; it is then placed 

 between that and the anterior layer or triangular ligament through 

 Avhicli it passes someway farther forwards, and has both of these fibrous 

 membranes prolonged upon it, the one backwards and the other for- 

 wards. Between these two layers the urethra is surrounded by erectile 

 tissue, by some veins, and also by the fibres of the compressor urethrce 

 muscle beneath it. On each side are Cowper's glands. The proper or 

 plain muscular fibres of this portion of the urethra are continued over 

 the outer and inner surfaces of the prostate into the muscular fibres of 

 the bladder posteriorly, and into those of the spongy portion of the 

 urethra anteriorly. (Hancock.) 



3. The spongy portion of the urethra, by far the longest and most 

 variable in length and direction, includes the remainder of the canal, 

 or that part which is surrounded by the erectile tissue of the corpus 

 spongiosum. Its length is about six inches. The part contained 

 within the bulb, sometimes distinguished as the hulhous iwrtion, or 

 sinus, is somewhat dilated. The succeeding portion, as far as the gians, 

 is of uniform diameter, being intermediate in this respect between the 

 bulbous and membranous portions. The cross section of its canal 

 appears like a transverse slit. The canal of the urethra, situated in 

 the glans has, on the contrary when seen in a cross section, the form 

 of a vertical slit : in this part, which is from four to six lines in length, 

 the canal is again considerably dilated, forming what is named the 

 fossa navicular is. 



Lastly, at its orifice, which is a vertical fissure from two and a half 

 to three lines in extent, and bounded by two small lips, the urethra is 

 again contracted and reaches its narrowest dimensions. From the 

 resistant nature of the tissues at its margin, this opening does not 

 admit so large a sound or catheter as even the membranous i3ortion of 

 the canal. 



The mucous membrane of the urethra possesses a lining of stra- 

 tified epithelium, of which the superficial cells are columnar, except 

 for some distance from the orifice, where they are squamous, and where 

 the subjacent membrane is beset with papillse. Outside the mucous 

 membrane there is a layer of convoluted vascular structure, and ex- 

 ternal to that a layer of plain circular muscular fibres separating it 

 from the proper substance of the spongy body. 



The whole lining membrane of the urethra is beset with small race- 

 mose mucous glands and follicles, commonly named the glands of Littre, 

 the ducts of which pass obliquely forwards through the membranes. 

 They vary much in size and in the extent to which their cavities are 



