URETHRA. 



1247 



the prostatic part of the urethra gradually de- 

 scends, until its general direction is more con- 

 tinuous with that of the membranous part. I 

 shall defer the description of the caput gal- 

 linaginis until I come to that of the general 

 surface of the urethra. 



The connection of the urethra to the pro- 

 state is very close, the ducts of the gland 

 passing directly into it ; it is therefore im- 

 possible to raise it from its attachment without 

 division of the prostatic ducts. When a ca- 

 theter is introduced, the course of the canal 

 invested by the prostate can be indistinctly 

 traced by the finger introduced into the 

 rectum. 



The membranous portion (pars muscularis, 

 isthmus urethra:) commences from the anterior 

 part of the prostate, and extends beneath 

 the arch of the pubis as far as the bulb : it is 

 included between the prostatic and spongy 

 portions, and is covered slightly at its anterior 

 and under part by the bulb, so that it is 

 really shorter below than above. It makes a 

 slight curve, the concavity facing upwards. 

 The concavity is at the distance of nearly an 

 inch from the interpubic substance ; the con- 

 vexity looks towards the perinaeum. Be- 

 tween it and the pubis, and just beneath the 

 pubic arch, the dorsal veins of the penis run. 



Proceeding from the anterior extremity of 

 the prostate, the membranous portion of the 

 urethra traverses the triangular ligament, 

 which splits into two lamella : one passing 

 backwards over the prostate, is continuous 

 with the capsule of the gland, the other ad- 

 vances forwards over the bulb, and blends 

 with the tendinous investment of the spongy 

 body. The opening through which the ure- 

 thra passes is round. The membranous por- 

 tion forms the segment of a circle, whose 

 radius is, according to Krause, 2 lines. This 

 part of the canal has been termed membran- 

 ous, from the idea that it represented a simple 

 membrane when deprived of its surrounding 

 muscular structure, and that it was wholly 

 destitute of any investment of the spongy 

 body. This, however, is not correct ; there is 

 a thin layer of vascular tissue, continuous in 

 front with the spongy body, and closely sur- 

 rounding the mucous membrane of this part 

 of the urethra, between it and its muscular 

 layers. The vessels of this extension of the 

 spongy body pass backwards, to terminate in 

 the plexus surrounding the neck of the blad- 

 der : this is mixed up with elastic tissue, and 

 constitutes a truly erectile tissue. An exten- 

 sion of the same structure enters into the for- 

 mation of the caput gallinaginis. 



Between the layers of the triangular liga- 

 ment, and in close connection with the mem- 

 branous part of the urethra, are found three 

 sets of muscular fibres (musculus urethralis] : 

 they consist of the two pairs of muscles de- 

 scribed, one by Wilson and the other by 

 Guthrie ; and the circular fibres of Santorini, 

 which closely surround the urethra. The 

 anteprostate, or Cowper's glands, covered by 

 the inferior stratum of the compressor urethrse, 

 are placed beneath this part, and the arteries 



of the bulb are in close approximation to it, 

 running beneath and on either side of it. The 

 floor of the membranous portion is traversed 

 longitudinally in the median line by the pointed 

 end of the caput gallinaginis. 



If a catheter be passed into the bladder, 

 the membranous portion can be distinguished 

 by the finger introduced into the rectum and 

 drawn forwards, there being only a small quan- 

 tity of cellular membrane interposed between 

 the under part of its muscular investment and 

 the intestine. 



Boyer estimated the length of the mem- 

 branous portion at about 1 inch ; Ducamp 

 from 9 to 10 lines ; Lisfranc found it in twelve 

 subjects to vary from 7 to 1 1 lines. In these 

 its anterior diameter varied from 3% to 4 

 lines, its posterior from 4^ to 5 lines, and just 

 behind the bulb it measured at least 1 line 

 less than in any other part. It is universally 

 admitted that the point of junction between . 

 the membranous and spongy portions is the r 

 narrowest part of the urethra, with the excep- 

 tion of the meatus. 



The membranous part of the urethra is sur- 

 rounded by muscular fibres, which have been 

 variously described by different anatomical 

 writers. Thus Santorini, as early as 1724, in 

 his Observationes Anatomicce, pointed out some 

 transverse fibres as encircling the urethra at 

 this part: he terms them " the elevator or eja- 

 culatorurethrae," and describes them as being 

 inserted into the lower part of the urethra. 

 Mr. Wilson, in the year 1808, gave a descrip- 

 tion of two muscles surrounding the mem- 

 branous part of the urethra, the origin of 

 which is from a tendon attached to the pos- 

 terior part of the symphysis pubis, a little 

 above its lower border: the muscle thus arising 

 from a single origin then descends, and divides 

 into two portions, which, reaching the mem- 

 branous portion of the urethra, spread them- 

 selves out by its side, and are implanted into 

 a common tendon below it. The muscle is 

 termed by Wilson the compressor urethrae. 

 In 1834, Mr. Guthrie, in his lectures at the 

 Royal College of Surgeons, demonstrated 

 another series of muscular fibres, as sur- 

 rounding the membranous portion of the 

 urethra, and of which he considers Wilson's 

 muscle as a part. That portion described by 

 Guthrie, and now known by his name, arises 

 by a thin tendon on either side, from the ra- 

 mus of the ischium, and, passing transversely, 

 splits into two portions, one above and the 

 other below the urethra; the two muscles 

 are connected together above by a mesial 

 tendon, which, passing forwards, is inserted in 

 part into the upper part of the urethra, whilst 

 another portion, passing backwards, is im- 

 planted into the upper surface of the front of 

 the prostate. The under portion of the muscle 

 is also connected with its fellow by a similar 

 mesian tendon, which, advancing forwards, 

 goes to the central tendon of the perinaeum, 

 and, sending a slip backwards, is inserted into 

 the under part of the prostate. 



The muscles are included between the two 

 layers of the triangular ligament j and the 



