538 MEMBRANOUS URETHRA. 



The discovery of this beautiful structure is due to our distin- 

 guished countryman, Sir Astley Cooper, and is one other instance 

 of the marvellous indications of design evinced in the structure of 

 the animal frame. Instead of a muscular apparatus, liable to fatigue, 

 Nature has employed, for the purpose of retaining the urine, an 

 elastic substance, which closes the urethra constantly by an unweary- 

 ing physical property. Expulsion, on the contrary, occurring only 

 at intervals, demands the exercise of muscular action, that action 

 being immediately applied to the elastic agent and drawing it aside. 

 It is by means of this interesting provision that the semen and the 

 last drops of urine are expelled from the urethra without a chance 

 of reflux into the bladder, and that the urine is enabled to pass freely 

 along its canal without danger of entering the prostatic or ejacula- 

 tory ducts. 



The Membranous portion, the narrowest part of the canal, is 

 somewhat less than an inch in length. It is situated between the 

 two layers of the deep perineal fascia, and is surrounded by the 

 fan-like expansions of the upper and lower segments of the com- 

 pressor urethras muscle' which meet at. the raphe along its upper and 

 lower surface. It is continuous posteriorly with the prostatic 

 urethra, and anteriorly with the spongy portion of the canal. Its 

 coverings are the mucous membrane, elastic fibrous layer, com- 

 pressor urethras muscle, and a partial sheath from the deep perineal 

 fascia. 



The Spongy portion forms the rest of the extent of the canal, and 

 is lodged in the corpus spongiosum from its commencement at the 

 deep perineal fascia to the meatus urinarius. It is narrowest in the 

 body, and becomes dilated at either extremity, posteriorly in the 

 bulb, where it is named the bulbous portion, and anteriorly in the 

 glans penis, where it forms the fossa navicularis. The meatus 

 urinarius is the most constricted part of the canal; so that a cathe- 

 ter, which will enter that opening, may be passed freely through the 

 whole extent of a healthy urethra. Opening into the bulbous portion 

 are two small excretory ducts about three quarters of an inch in 

 length, which may be traced backwards, between the coats of the 

 urethra and the bulb, to the interval between the two layers of the 

 deep perineal fascia, where they ramify in two small tabulated and 

 somewhat compressed glands of about the size of peas. These are 

 .Cowper's glands ; they are situated immediately beneath the mem- 

 branous portion of the urethra, and are enclosed by the lower seg- 

 ment of the compressor urethras muscle so as to be subject to mus- 

 cular compression. Upon the whole- of the internal surface of the 

 spongy portion of the urethra, particularly along its upper wall, are 

 numerous small openings or lacunas which are the entrances of 

 mucous glands situated in the submucous cellular tissue. The 

 openings of these lacunae are directed forwards, and are liable occa- 

 sionally to intercept the point of a small catheter in its passage into 

 the bladder. At about an inch and a half from the opening of the 

 meatus one of these lacunas is generally found much larger than the 



