in anatomy, a thin expanded membranous body, found in several parts of an animal, serving as a receptacle of some juice, or of some liquid excrement; from whence it takes various denominations, as urine-bladder, gall-bladder, &c.

Bladder, by way of eminence, is a large vessel which serves as a receptacle of the urine of animals, after its secretion from the blood in the kidneys. This is sometimes also called, by way of distinction, the urinary bladder, vesica urinaria. The bladder is situated in the pelvis of the abdomen; in men immediately on the rectum; in women on the vagina uteri. See Anatomy.

Though the urinary bladder be naturally single, yet there have been instances of nature's varying from herself in this particular. The bladder of the famous Calabon, upon dissecting his body after his death, was found to be double; and in the Philosophical Transactions, we have an account of a triple bladder found in the body of a gentleman who had long been ill and no one could guess the cause.

The urinary bladders of brutes are differently contrived from the human bladder, and from each other according to the structure, economy, and manners of living of each creature. See Comparative Anatomy.

Bladders, when below a certain magnitude, are more usually denominated by the diminutive vesicles, vesicule. Of these we meet with many forms both in the animal and vegetable world; some natural, as in the lungs, especially of frogs, and as some also imagine, in the mucilages; others morbid or preternatural, as the hydatidus, and those observable in the itch. Naturalists have also discovered bladders in the thorax and abdomen of birds, as well as others in the belly of fishes, called air-bladders and savins.

Vegetable bladders are found everywhere in the structure of the bark, the fruit, pith, and parenchyma or pulp; besides those morbid ones raised on the surface of leaves by the puncture of insects.