The exact arrangement of the muscular fibres at the neck of the bladder has not been very accurately explained ; some describe them as arranged circularly so as to constitute a true sphincter : this opinion is maintained by John Bell, System of Anatomy, vol. iv. p. 159 ; also by Palfin, Anat. torn. i. p. 163 ; by Meckel, Anat. vol. iii. p. 564 ; by Bayle and others. Sir Charles Bell also describes a sphincter vesicw to exist, but places it in a different situa tion from that usually assigned. His description of this muscle is as follows :—" to exhibit it, cut off all the appendages to the bladder except the prostate gland, make an incision into" the fundus and invert it, dissect off the inner mem brane from around the orifice of the urethra ; a set of fibres will be discovered on the lower half of the orifice running in a semicircular form round the urethra ; these make a band of about half an inch in breadth, particularly strong on the lower part of the opening, and having mounted a little above the orifice on each side, they disperse a portion of their fibres in the substance of the bladder; a smaller and weaker set will be seen to complete their course surrounding the orifice on the upper part, to these sphincter fibres a bridle is joined which comes from the union of the muscles of the ureters ; this is the most posterior part of all the muscles which embrace the urethra, it re sembles the sphincters of the other hollow vis cera; for example, that of the pyloric orifice of the stomach."'' The great advantage of the sphincter as thus described must be, as Sir C. Bell says, to prevent the fluids from the seminal vessels and from the ducts of the prostate gland, falling back into the bladder, as also to protect the ori fices of these ducts from exposure to the urine when the bladder is closed, and that without this arrangement it would be inconceivable how the contents of the vesiculaa seminales could be discharged forwards, or how the urine could be retained while the seminal discharge was being made. We must remark, that after frequent examinations of this region, we cannot satisfy ourselves of the existence of this particular ar rangement, although we are convinced that the orifice is furnished with a sphincter such as we shall presently describe. Moreover, we believe that the prostatic secretion is more or less ex pressed at each evacuation of the urine, inas much as the longitudinal, the principal detrusor fibres of the bladder, are fixed into, expand upon, and must compress this gland, especially at the commencement of the process, although they obviously can have no effect on the vesi culte seminales, vasa deferentia, or their contents.
The existence of a true muscular sphincter is denied by Sabatier, Anat. tom. ii. p. 403; Marjolin, torn. ii. p. 473; also by Bichat, Anat. desc. torn. v. p. 147 ; by Boyer, Anat. torn. iv. p. 490 ; by Cloquet, Anat. tom. ii. p. 1050; by Portal, Anat. torn. v. p. 401; the latter, however, describes the urethral orifice as surrounded by oblique muscular fasciculi. Winslow also, Anat. torn. ii. p. 210, denies a true sphincter, but ascribes the office of such to the muscular fasciculi which pass from the pubis to the bladder. Wilson (Lectures on the Urinary and Genital Organs, p. 57,) denies the existence of any regular sphincter, but thinks, from the distribution of some fibres at the beginning of the urethra, and which pass round it semicircularly from the forepart and meet the descending fibres behind, that the contraction of these, assisted by those of the urethra nearer the penis (compressores urethrae), may be considered as sufficient to prevent the urine passing from the bladder into the urethra. Several of the foregoing writers who deny a muscular sphincter to the bladder, consider, nevertheless, that its orifice is closed by a pe culiar tissue which resists the ordinary tendency of the muscular coat to expel its contents, but which is capable of yielding to the increased force which is exerted in the ordinary evacua tion. Thus Bichat describes, as placed between the mucous lining and the external cellular tissue, a dense white fibrous substance, con tinuous with the muscular fibres which are in serted into it, a small process of this prolonged posteriorly to the uvula, and another anteriorly to the verumontanum. This substance is not muscular, and presents a passive organic resistance. Cloquet, Boyer, and Marjolin con cur in the same account ; it is difficult, how ever, to reconcile with such a condition of parts the phenomena which not unfrequently occur in disease, such as paralysis and incontinence of urine in cases of injury of the spine, or of the nervous system ; or again, retention of urine from irritation in this situation caused either by local inflammation, or through sympathy with some adjacent diseased organ, or by some pe culiar acrimony in the urine. A muscular struc ture is more reconcilable with these, and with many other pathological facts, than an elastic, or fibrous, or resisting tissue, such as this part is stated to be furnished with. The result of our
examination convinces us that the organization of this part is very peculiar, and that the. neck of the bladder is closed by a power more than that of a mere elastic tissue. Elasticity no doubt resides in this structure, and we admit to a con siderable extent, as it does in almost every ant mal tissue, except perhaps mucous membranes: elasticity exists at the pylorus and at the anus, although true muscular and sphincter fibres are evident at both these outlets. When this region is carefully examined in the male subject, we shall find that immediately behind the pubis, on the anterior and lateral reflections of the pelvic fascia, to these ligaments numerous muscular fibres of the bladder are attached ; these are chiefly longitudinal, but there are also several transverse arched or semilunar, some upon, and others underneath the longitudinal fibres, and with which many of them are continuous. None of these arched fibres pass around or behind the prostate so as to encircle this region. The longi tudinal, the transverse and decussating or inter lacing fibres in this situation, are in greater abundance, and may be raised in successive laminae. Veins and nerves are very manifest in and between these ; several of the longitudinal fibres of the deeper laminae pass in so deeply as to approach the mucous surface. When the several strata of longitudinal fibres have been raised from the front and lateral parts of this region, the circular fibres of the bladder become distinct, but do not appear so proportionably increased as were the longitudinal ; but on de taching more completely the longitudinal strata down to the circumference of the very opening of the urethra, a distinctly fibrous, that is, mus cular tissue, is evident, bounding this opening laterally and superiorly, but not below. This muscular fasciculus is not intimately connected to the general circular coat ; it appears redder, and of a closer texture, and will be found to be attached to the fibrous or tendinous substance forming the anterior part of the trigone on each side of the uvula, behind which it does not pass. The longitudinal fibres are inserted partly into this semicircular muscle, much in the same manner as the levatores ani are inserted into the circumference of the anus. This structure we consider to be partly elastic, but essentially muscular; it bounds the urethral opening late rally and above, but not below; the slight pro jection of the uvula in the latter situation, and the elasticity and gentle state of contraction natural to all the sphincter muscles, will pre serve this opening in a constantly closed state during the quiescent and normal condition of the parts. This arrangement is on a level with the uvula, and, of course, behind the orifices of the prostate ducts, although the base of that gland extends further back than this sphincter. We have repeatedly examined beneath the uvula for muscular fibres, but have found none in a transverse direction ; there is, therefore, no portion of a sphincter in that spot, and hence one advantage of the slight elevation caused by the uvula and by that portion of the prostate gland denominated its middle lobe, which cor responds to it : indeed sphincter fibres in this spot would be not only useless, but injurious, as they could scarcely exist without interfering with the ejaculatory ducts. We conceive, then, that the urine is retained in the bladder partly by relaxed or passive state in which its muscular coats usually remain until they are excited by the sense of distension, partly also by the urine, when only in a moderate quantity, gravitating, not towards the neck, but distending the inferior fundus, which lies on a level lower than that of the former, and principally by the dense muscular, elastic, vascular, and nervous tissue which surrounds three-fourths of the orifice of the bladder. The gentle contraction of the latter raises the uvula into the calibre of the opening, while the remaining sides are pressed into contact with it, and thus the bladder is closed. When distension excites the usual feel ing, the muscular coat contracts, the sphincter relaxes, phenomena exactly corresponding to those which take place under similar circum stances in the rectum and anus ; and as the levatores ani expand the anal opening by draw ing the sphincter fibres outwards at the time the expulsive powers of the rectum are dis charging its contents, so the longitudinal fibres of the bladder draw out from the axis of the urethral opening the relaxed sphincter which encompasses three-fourths of it, while the middle band of the posterior longitudinal will plainly depress the uvula and expand the orifice in that aspect, and will even retract and depress the verumontanum, thereby freeing the passage into the urethra, and retracting that sentient caruncle from the irritating influence of the urinary stream.