Bladder, a musculo-membranous bag, cyst, or pouch, which serves as a reservoir for the urine secreted in the kidneys. It is called vesica urinaria, to distinguish it from the gall bladder, a small cyst connected with the liver and the biliary ducts as a reservoir for bile. The bladder is situated in the pelvis, immediately behind the symphysis pubis, and in front of the rectum or terminal portion of the intestines in the male - in front of the uterus and vagina in the female. Thus placed in the lowest portion of the trunk in front, it communicates by means of two long tubes called ureters with the two kidneys, placed high up in the back, just above the lumbar region, on each side of the vertebral column. It communicates with the exterior by means of a single tube called the urethra, through which the urine is voided. In infancy it is of a pyriform shape, and situated almost entirely in the abdomen; it undergoes a change of form in the adult, and sinks deeper in the pelvic cavity. It then assumes the shape of a short oval, compressed in its anterior and posterior walls: its lower surface expands on the rectum, and forms what is termed by anatomists the bas-fond of the bladder.

In the female its transverse diameter is greater than it is in the male, owing to the position of the uterus and vagina between the bladder and the rectum. It increases in dimensions with advancing age, and is larger in females than in males, probably from habitual distention, arising from constraint. The direction of the bladder is oblique, being inclined forward and upward. It is retained in its position by ligaments. Anatomists have divided it into six regions or surfaces, for the facility of description and surgical operation; these are named anterior, posterior, superior, inferior, and left and right lateral. The anterior surface lies behind the symphysis pubis, with which it is connected by loose connective tissue. When distended, the bladder rises, and its anterior surface comes in contact with the recti muscles of the abdomen. The posterior surface is covered by the peritoneum, which is reflected upon it from the rectum in the male, and from the uterus and vagina in the female. The lateral and superior regions are partially covered by the peritoneum. The inferior region, or bas-fond, is the most important in a surgical point of view. It is bounded before by the prostate gland, and behind by the peritoneum.

Attached to it in the male we find the vesiculce seminales and the vasa deferentia, which converge to the prostate gland, leaving a triangular space, where the bladder is only separated from the rectum by a quantity of fatty connective tissue surrounding numerous small vessels, chiefly veins. In the female this region rests on the vagina, which separates it from the rectum. The anterior and inferior regions of the bladder being left uncovered by folds of the peritoneum, the surgeon is able to perform operations on those parts without injuring that membrane, which is so liable to dangerous inflammation from wounds. - The walls of the bladder are composed of three layers or coats, united by connective tissue: an internal or mucous membrane, a middle or muscular coat, and an external or serous coat, formed by folds of the peritoneum. The muscular coat is composed of pale fibres interlacing in all directions, and enabling the bladder to contract so perfectly as to expel every drop of its contents. The neck of the bladder differs in structure from the rest of the organ, being composed of a somewhat fibrous whitish substance, and forming a connecting medium between the bladder and the urethra.

Its posterior part rests upon the rectum; its anterior is surrounded below and at the sides by the prostate gland, which is peculiar to the male. This gland is composed of an aggregation of mucous follicles, forming three lobes, one on each side of the neck of the bladder, and one below, communicating by means of small ducts with the urethra. The inner coat or lining of the bladder, being a portion of the genito-urinary mucous membrane, not only lines the bladder, but is prolonged upward through the ureters into the kidneys, and downward along the urethra. It is of a pale rose color, with a smooth surface when the bladder is distended, and corrugated when empty. This membrane secretes a viscid fluid termed mucus, which protects it from the acrimony of the urine with which it would otherwise be in contact. - The secretion of the urine is performed by the kidneys, which are constantly active, without any apparent alternation of action and repose, although within a given period they do more work at one time than another.

The urine thus secreted dribbles incessantly along the ureters, and drops into the bladder, where it accumulates until the walls are distended, and a general uneasy sensation is produced which calls for an evacuation of the contents. - Congenital malformations of the bladder are not unfrequent. Sometimes it is altogether wanting; and in such cases the ureters empty into the rectum, as into the cloaca of birds, or at the pubes, or directly into the urethra. A still more frequent malformation is that in which, the lower portions of the recti muscles being imperfect, and the anterior wall of the bladder deficient, the posterior wall is protruded and forms a red fungus-like tumor above the pubes. The tumor presents two orifices, which are the mouths of the ureters, from which the urine constantly dribbles. Blasius describes a case in which the bladder was double. Molinetti, it is said, found in a female subject five kidneys, five ureters, and five bladders. - Inflammation may affect the coats of the bladder singly or together. When the mucous membrane is inflamed, there is a sense of irritation and a constant desire to discharge the contents. Ulcers, gangrenous spots, and indurations of various kinds may be produced by inflammation.

The secretion of the mucous membrane may be increased or altered, constituting what is termed catarrh of the bladder. The mucous membrane is sometimes found in a varicose state. In other cases it gives origin to cysts of different kinds, and fungous growths; the latter occur mostly in old people. Various accidents and diseases may prevent the bladder from evacuating its contents, in which case it becomes excessively distended, and unless relieved inflammation ensues, a portion mortifies, through which the urine escapes into the abdomen, and speedy death is the result. After three days' retention the bladder usually attains its utmost limits of distention, and if not relieved the contents are evacuated in small quantities, as they would be in a case of mere incontinence of urine; and it is of great importance therefore not to mistake retention for incontinence where there is this point of similarity in their respective symptoms. When there is danger in delay, and a catheter cannot be introduced, the bladder may be punctured, either through the perineum or the rectum, or above the pubes, as it is not covered by the peritoneum in these regions. - Where urinary calculi exist in the bladder, they are removed by surgical operations.

When small, they may be extracted through the urethra by a pair of forceps invented for the purpose; when large, they may sometimes be reduced into small pieces, minute enough to pass away with the urine; and where this is not practicable, they may be removed by cutting into the bladder. - In the whole class of birds there are no urinary bladders; the ureters descend from the kidneys and open into the cloaca, a musculo-membra-nous bag, which takes the place of the rectum, the uterus, and the bladder of the higher animals, and serves as a reservoir for solid excrement, for urine, and for eggs. In these animals the urine dilutes the faeces and forms the carbonate of lime or hard substance of the shell. The urinary bladder exists in several genera and species of fishes.