URETHRA. 



1249 



membrane, not unlike the fourchettc of the 

 female labia. 



The urethral orifice is surrounded, accord- 

 ing to Guthrie*, by a peculiar dense struc- 

 ture, which he considers analogous to that 

 which forms the edge of the eyelid, and which 

 he believes to be requisite to maintain the 

 patency of the opening ; for if this be de- 

 stroyed by ulceration, the part from which it 

 has been removed contracts, and the opening 

 becomes so small, as to give rise to a most 

 troublesome form of stricture. The opening 

 of the urethra is almost invariably the nar- 

 rowest part of the canal ; and hence, if an 

 instrument has been introduced through this, 

 it will with facility traverse the remainder of 

 the passage, unless there be some mechanical 

 impediment from spasm or disease ; and hence 

 a trifling division of this part will permit the 

 passage of a large instrument, and the escape 

 of fragments of stone, which are frequently 

 arrested here after the operation of lithotrity. 

 It is but sparingly elastic. After immersion 

 in alcohol, the mucous membrane at the meatus 

 urinarius will be found arranged in circular 

 folds. 



In briefly reviewing the condition of the 

 urethra as connected with the structures in- 

 vesting it, we observe that the prostatic por- 

 tion, being surrounded by a body possessing 

 considerably dilatability, remains under almost 

 every condition passive and yielding; and hence 

 it happens that a catheter, having reached this 

 part of the canal, must, if its point be properly 

 directed, enter the bladder, unless there be 

 some enlargement of the prostate itself; and 

 hence the inference that no force is to be 

 employed in passing the catheter under these 

 circumstances. 



On the contrary, the membranous portion 

 of the urethra is a part of high irritability. 

 This depends partly on the nature of the tissue 

 itself, but mainly on the muscular apparatus 

 connected with it. This part of the canal is 

 most liable to irritation and spasm from general 

 and local causes ; and is well known to be 

 the most frequent seat of stricture. The 

 remainder of the urethra is entirely sur- 

 rounded by the corpus spongiosum, and must 

 necessarily be influenced by the condition of 

 that body. When the latter is distended, as in 

 erection, the diameter of the urethra must be 

 proportionally diminished ; and, in the undis- 

 tended state of the former, it assumes its 

 greatest degree of dilatability. Consequently, 

 in the introduction of the catheter, the chief 

 difficulty, even independent of organic disease, 

 is experienced at the meatus, or at the angle 

 formed at the junction of the bulb and anterior 

 part of the spongy portion, or at the mem- 

 branous part, the remainder of the spongy por- 

 tion in the healthy state seldom offering any 

 resistance to the progress of the instrument. 



It will also be further remarked, that the 

 dorsal surface of the urethra is smooth and 

 even throughout, except in the situation of the 

 lacuna magna, whilst its depressions and eleva- 



* Lectures on Diseases of the Bladder and 

 Urethra. 

 VOL. JV. 



tions are found upon the floor of the canal, 

 and hence the importance in catheterisation of 

 keeping the beak of the instrument against the 

 superior part of the urethra. 



.Mucous Membrane. The urethra is es- 

 sentially a mucous canal, forming an important 

 part of the genito-urinary mucous system. 

 It is continuous with the mucous mem- 

 brane of the bladder, and blends at the meatus 

 with the cutaneous covering of the glans 

 penis. There is always a distinct line of de- 

 marcation at this part, the urethral surface 

 being moistened by a mucous secretion. When 

 laid open, it can be frequently seen to present 

 two distinct white lines, one at the upper, and 

 the other at the under surface, running longi- 

 tudinally ; these are supposed to indicate the 

 original lateral division of the canal. Inde- 

 pendent of this, the mucous membrane will 

 be generally found arranged in longitudinal 

 folds, with furrows between them. The folds 

 vary in depth and breadth, the larger are! 

 found on the under surface, and they are 

 more numerous in this situation than above. 

 They commence at the bulb and. run forwards, 

 sometimes continuing of the same size through- 

 out, frequently tapering and sending off, as 

 they approach the extremity of the penis, 

 delicate processes, which present a somewhat 

 arborescent arrangement, not unlike that pre- 

 sented by the lining membrane of the uterus ; 

 many on the dorsal aspect will be seen to 

 terminate on either side of the lacuna magna. 

 The folds of the urethra, which are not al-f 

 ways visible after death, result from the con -I 

 traction of the submucous layer, and are sol 

 arranged, that, when the two surfaces are in ap- 

 position, especially if the vessels of the urethra 

 be injected, a sort of dovetailing of the mucous 

 membrane occurs, bearing a slight resemblance 

 to the plicated arrangement of the oesophagus 

 of the whale. 



The urethra after death is whitish in colour, 

 and in some parts so transparent as to permit 

 the veins of the corpus spongiosum to be 

 seen through it. Its bloodvessels are readily 

 injected, when the whole canal presents a beau- 

 tiful vermilion tint. At the membranous por- 

 tion, Shaw has described a considerable plexus 

 of veins beneath the mucous membrane of the 

 urethra: these veins are spread all over the 

 canal, but are accumulated at the membranous 

 part, lying one over the other in its long axis, 

 so as to form two distinct columns with a 

 groove between them : they unite and sur- 

 round the sinus pocularis. Wilson had ob- 

 served this arrangement of vessels, before 

 Shaw published his description of them. 

 These veins communicate with the plexus 

 surrounding the prostate and neck of the 

 bladder. They are best seen by inserting a 

 tube beneath the mucous membrane, and in- 

 jecting them with mercury. Shaw supposes 

 them capable of considerable distension, and 

 thus of producing a species of erection of this 

 part of the tube.* In rude attempts to pass 

 a catheter, the vessels of this part are often 



* Medico-chirurg. Trans, vol. x. 

 4-L 



