The next coat of the bladder, the fourth of some anatomists, or the second common of others, is the deep cellular, or more properly the submucous cellular coat, by some also de nominated the nervous tunic. This coat invests the whole organ and connects the muscular and mucous tissues intimately yet loosely ; it con tains no adipose matter, but is very filamentous, extensible, and elastic : in it are found those vessels and nerves which are to supply the in ternal surface of the bladder, and which, except in some situations, are not very numerous when compared with those in the other hollow vis cera. This coat, though essentially cellular, pre sents very many fibrous threads through it, on which much of its strength appears to depend, particularly in those places where the muscular coat is deficient. When the bladder is fully distended, if we dissect off the muscular fibres carefully without injuring this tissue, the mu cous membrane still remains supported ; but as soon as a portion of this coat is detached, the mucous membrane projects in an unsup ported sacculated manner. This coat corre sponds with that elastic tissue in the parietes of the small intestines in some animals, out of which the substance, commonly termed catgut, is formed.
The third proper coat is the mucous or lining membrane, to expose which the bladder must be opened by a perpendicular incision along its anterior region. This tunic is but a portion of the genito-urinary mucous membrane, and is continuous with that lining the ureters above, and the urethra below. The vesical portion of this membrane is very thin, has a soft and smooth feel caused by the mucous fluid which lubricates it ; its colour is very pale in the natural condition, although in catarrh or in chronic inflammation it presents a general vascular appearance ; but in health the mucous surfaces of the intestinal tube and of this organ form a strong contrast, more particularly if the vessels of Loth have been injected with coloured size; the former will then assume the colour of the injection, the lat ter will continue pale, although numerous ves sels become apparent in the submucous tissue. The mucous lining of the bladder in the healthy state does not present any distinct follicles or cryptee except near the cervix, which become very distinct in chronic disease. A cuticular or epidermoid covering cannot be detected in health, although in certain states of disease a substance very similar to cuticle is occasionally discharged in shreds and flakes. When the blad der is empty and contracted, the mucous mem brane is thrown into numerous rugaa, existing chiefly in a transverse direction, which are most distinct if a very recently contracted bladder be examined. When the organ is distended, these Fugue disappear, so that their existence may be considered as evincing a want of elasticity in this tissue. This membrane presents some pecu liarities throughout the extent of a small region named the trigone' or the velum' of the bladder: this term is applied to a small triangular space, nearly equilateral, situated about the middle of the inferior region, and leading to the neck of the bladder. The base of this space is a lunated line 'leading from the orifice of one ureter to the other ; the sides are marked by lines which converge forwards from these open ings to a slight projection at the neck of the blad der named the uvula,' which is immediately behind or rather in the orifice of the urethra. Throughout the area of this space the mucous membrane is very smooth and free from rugu or folds, as it adheres closely to the fibrous or compact cellular substance beneath : it is also more vascular, being generally of a delicate rose colour, or variegated with fine vessels, and when minutely examined with a magnifying lens numerous fine villi can be discerned. On the whole this surface appears to be delicately and peculiarly organized, and no doubt possesses higher sensibility than the remainder of the in ternal surface of the organ. The posterior part of the trigone is thinner than the anterior ; the line which marks its base is a thickened band of the circular or transverse muscular fibres, behind which the inferior fundus of the bladder is fre quently dilated into a pouch which presses against the rectum, and where a calculus some times rests, so as to elude the search of the sound unless the finger be introduced into the rectum : in old persons this pouch sometimes remains constantly full of urine, the muscular coat of the bladder not being able to contract it. The lines which form the sides of the tri gone, and which extend from the orifices of each ureter to the uvula, are composed of a slight projection of the mucous membrane, be neath which is some cellular tissue, and in some cases a few pale muscular fibres are dis tinctly seen. These lateral lines are not in
general very distinct, at least in the healthy bladder; their distinctness is owing to little more than being the borders of this space. In some cases, particularly when the prostate has been enlarged or the urethra obstructed, they are found very distinct, the muscular fibres they contain being thickened even in a greater degree than the other portions of the muscular coat of the bladder. These lateral fasciculi appear to be little more than some of the lon gitudinal muscular fibres of the bladder con verging towards its cervix. Sir C. Bell, however, has attached a particular importance to these muscles, he denominates the GC muscles of the ureters :" his description of their attachments and use is as follows, in his own words :—" The use of these muscles is to assist in the contraction of the bladder, and at the same time to close and support the mouths of the ureters." " They guard the orifices of the ureters by preserving the obliquity of the passage, and by pulling down the extremities of the ureters according to the degree of the con traction of the bladder generally." It appears very questionable how far this statement as to the structure of these lines is generally, correct, and it is still farther doubtful whether the use assigned is correctly ascribed or not ; for it may be remarked that these lines are often very faintly traced, that the muscular structure. within them is sometimes very in distinct, that in females it is scarcely observable, in very young children also of either sex it is not well developed ; whereas if such an import ant office as that of guarding the ureters de pended on these muscular fibres, it is most probable, and indeed is even certain that their presence would be constant and their deve lopment more uniform. Again, the fact of the dead bladder when fully distended with fluid, or even with air when the urethra is tied, and the contents not escaping through the ureters, is a strong proof that the oblique or valvular direc tion of the latter is the true cause of the non regurgitation, and that it does not depend on the contraction of any particular muscular fibres. Again too, in animals this structure, as described by Sir C. is not at all obvious although the ureters have the same oblique course as in man ; it would rather appear that these muscular bands, which are occasionally very distinct along the sides of the trigone, are only portions of the longitudinal fibres, and that their action iv-ill be to shorten the trigone, to draw its base forward, and thus to assist in emptying the bladder. They may doubtless assist in fixing the orifice of the ureters and moving these in proportion as the surrounding parts an affected, but the opinion that the preservation of the valvular or oblique course is depending upon them appears to be invalidated by the fore going remarks, as well as by the following expe riment. The healthy bladder of an adult male, recently dead, was opened to a small extent on its fore-part, and the sides of the trigone were cut by a sharp-pointed bistoury passed beneath each of them ; the urethra was then tied, and the bladder carefully closed : its cavity was next fully distended with water, and the fluid was retained for a considerable time although it was subjected to pressure, and was afterwards eva cuated through the urethra when the ligature on the latter was removed. No alteration whatever from the ordinary appearances was observed either during the distension or the subsequent emptying of its cavity, nor did any regurgi tation take place into the ureters in either state. The same experiment with air instead of water was repeated and with the same effect. It may be further observed that the ductus communis choledochus enters the duodenum in a similar oblique way, that no regurgitation from the intestine ever occurs into it, and yet there is no peculiar muscular fasciculus attached to its orifice which could execute the office ascribed to these lateral boundaries of the tri gone. To these muscles Sir C. Bell also attributes the projection into the bladder, of the third lobe of the prostate gland, usually called the middle or Home's lobe, when this part is in a state of enlargement. There are, however, such plain and simple reasons for this tumour be coming prominent in this direction rather than in any other, that it is unnecessary to search for an explanation in the action of these muscles, the undoubted development of which in such cases may with a much greater degree of pro bability be considered as one of the effects and not as the cause of this projection.