PERINEUM. 



925 



of the vas deferens becomes continuous with 

 that which carpets the urethra at the orifice of 

 the common ejaculatory duct. 



The membranous portion of the urethra is 

 intermediate between the prostatic and the 

 spongy portions of that canal. In situ its 

 length seldom exceeds three quarters of an 

 inch, but when detached and extended it ap- 

 pears about an inch long. Its direction is nearly 

 horizontal, but its upper surface presents a very 

 slight curve, concave towards the pubis. Its 

 under surface is overlapped from before by the 

 bulb, a disposition which diminishes somewhat 

 the apparent length of its lower wall. Its 

 anterior extremity is fixed by the triangular 

 ligament of the urethra, a structure of uncom- 

 mon strength, through which it passes ; but 

 posteriorly it projects behind the triangular 

 ligament for a short distance, and being there 

 girded by Wilson's muscles, which support it 

 like a sling, it possesses in that situation con- 

 siderable mobility. The membranous portion 

 of the urethra is naturally the narrowest part of 

 the canal, presenting in this respect a marked 

 contrast to the prostatic and spongy portions. 

 Its parietes are endowed with considerable 

 powers of resistance, being strengthened in 

 front by the triangular ligament, which sends 

 forwards upon them an expansion continuous 

 with the fibrous covering of the bulb; whilst a 

 still stronger expansion derived from the back 

 of the triangular ligament surrounds the urethra 

 beneath Wilson's muscles, and affords it power- 

 ful protection posteriorly. Between this latter 

 investment and the mucous membrane a pecu- 

 liar structure exists of which the exact nature 

 is rather doubtful, some considering it a modi- 

 fied erectile tissue, whilst others look upon it as 

 muscular. 



The membranous portion of the urethra 

 merits from the surgical anatomist an attentive 

 consideration. It is here that the operator lays 

 bare the groove of the staff in lithotomy per- 

 formed after the lateral or bilateral methods ; 

 this is the situation in which spasm usually 

 arrests the catheter, the obstruction being pro- 

 duced by undue action of Wilson's muscles. 

 Foreign bodies, such as calculi, are very likely 

 in consequence of its diminished calibre to be 

 impacted in this part of the canal, and its 

 anterior extremity is frequently the site of per- 

 manent stricture. 



In using a curved catheter the surgeon should 

 slacken the penis upon the instrument so soon 

 as its point has fairly traversed the triangular 

 ligament; for if, during the further depression 

 of the handle, the penis be forcibly stretched 

 upon the catheter, its point may push the upper 

 wall of the urethra against the back of the 

 pubis, and in that manner produce considerable 

 mischief. It is also of advantage to communi- 

 cate a slightly onward movement to the catheter 

 at this part of the passage, as the bladder is 

 situated much more posteriorly, and in the 

 introduction of any instrument, whether curved 

 or straight, it should be borne in mind that 

 spasmodic obstructions yield in general to gentle 

 but continued pressure, and that attempts to 

 force such strictures are usually productive of 



increased spasm, and, if persisted in, of lacera- 

 tion of the urethral canal. 



In connexion with the perineum, so much of 

 the spongy portion of the urethra only as is 

 covered by the acceleratores urinse muscles re- 

 quires to be considered, and of this the bulb 

 constitutes the largest and most important part. 

 The bulb is an oval swelling, in which the 

 corpus spongiosum urethras commences poste- 

 riorly, it varies in size according to the sub- 

 ject, being small during childhood, enlarging 

 very much at puberty, and often presenting 

 excessive dimensions in old men ; during erec- 

 tion, too, it is turgid and swollen, though at 

 other times it remains comparatively flaccid. The 

 length of the bulb, when well developed, may be 

 estimated at an inch and a half, and its thickness 

 or depth from the cavity of the urethra at about 

 eight lines. Its posterior extremity is thick and 

 overlaps the membranous portion of the ure- 

 thra, whilst anteriorly the bulb becomes gra- 

 dually narrower, but there is no exact line of 

 demarcation between that body and the re- 

 mainder of the corpus spongiosum. The bulb 

 is situated between the crura penis and in front 

 of the triangular ligament of the urethra, to 

 which it is connected by the expansion of 

 fibrous membrane already described ; it is co- 

 vered by the acceleratores urinae, and derives 

 from them a muscular sheath all but perfect. 

 The bulk of this body is constituted by a 

 spongy erectile tissue, remarkably soft, and 

 possessing intrinsically little powers of resist- 

 ance, but a thin fibrous membrane of invest- 

 ment affords it some protection from without. 

 The canal of the urethra in this situation pre- 

 sents a slight dilatation (most observable infe- 

 riorly) named the sinus of the bulb, and the 

 delicate ducts of Cowper's glands, two in num- 

 ber, open into the lower and lateral parts of the 

 passage still further forwards. It should be 

 particularly noted that the bulb, measured at 

 the exterior, is in point of size quite out of 

 proportion to the width of the corresponding 

 part of the urethral canal, the canal presenting 

 but a slight dilatation, whilst the dimensions of 

 the bulb are very considerable ; and of equal 

 importance in practice is the fact that the axis 

 of the bulb differs widely from the axis of the 

 corresponding portion of the canal, the axis of 

 the bulb running in a very oblique direction 

 downwards and backwards towards the lower 

 extremity of the rectum, whilst the axis of the 

 canal lies upon a higher plane and runs much 

 more nearly horizontally backwards. 



In a healthy urethra the principal difficulties 

 of catheterism, whether performed by straight 

 or by curved instruments, are encountered at 

 this part of the passage : the sudden change 

 in direction which the urethra here undergoes, 

 the abrupt nan-owing of the membranous por- 

 tion immediately behind the dilatation of the 

 bulb, the mobility of the urethra in front of 

 the triangular ligament, and its immobility 

 where it passes through that structure, the ease 

 with which a catheter perforates the delicate 

 tissue of the bulb, and, above all, the striking 

 difference in direction observable between the 

 axis of the bulb and the axis of the correspond- 



