The bladder, like the other hollow viscera, is composed of three layers, or coats, united to each other by cellular tissue; these coats are the peritonmal or serous, the muscular, and the mucous. The peritonwal coat has been already described as investing only a portion of the organ ; it is united to the muscular coat by cellular tissue, which is extended over the whole of the latter, being however thinner under the peritoneal coat than elsewhere. The muscular coat has been described by some anatomists as a distinct ;manacle under the name of detrusor mime ; it is composed of pale fibres interlacing in all directions. Three distinct layers have been described, but it is sufficient for all useful purposes to say, that the superficial fibres are directed in the course of the axis of the bladder; that at the sides they are more and more oblique ; and that the more internal fibres assume a circular direction as they approach the neck of the bladder, so that some anatomists have described them in this part as a distinct muscle, under the name of sphincter vesiew. This reticulated structure of the muscular coat enables the bladder to contract so perfectly as to expel every drop of its contents.
When the bladder is much distended, the muscular coat becomes attenuated to such a degree, that it is difficult to distinguish it from cellular tissue. Sometimes its fibres become so much enlarged from the effects of long-continued irritation and overaction of the organ, that they forum projecting lines or columns under the mucous coat ; this appearance of the bladder is dessignated by the French Vessie h Colonnes. The mucous membrane is occasionally protruded between these columns, forming saes, or pouches, in which urinary calculi are sometimes lodged; these calculi are then said to be encysted or sacculated. The muscular coat is united to the third, last, or mucous coat by a distinct layer of cellular tissue, to which the term nervous or vascular coat is sometimes improperly applied. The mucous coat, or lining of the bladder, belongs to that division of the mucous membranes denominated genitourinary; it not only lines the bladder, but is prolonged upwards along the ureters into the kidneys, and downwards along the urethra ; it is of a pale rose-colour, is smooth when the bladder is distended, and corrugated when it is empty ; it secretes a viscid fluid termed mucus, which protects it from the acrimony of the fluid with which it is constantly in contact. Three openings are seen in it ; two situated posteriorly, about an inch and a half from each other, which are the openings of the ureters, and one anteriorly, which is the opening of the urethra. Extending from the openings of the ureters to that of the urethra are observed two prominent lines, which are formed by muscular fibres elevating the mucous coat ; these hues form the sides of a triangle, the base of which is an imaginary line drawn between the openings of the ureters the apex is at the urethra. The space thus marked out is denomi
nated the trigone vesicale ; it is paler than the rest of the internal surface of the bladder, in possessed of peculiar mensibility, and is smooth in the contracted as well as in the distended condition of the bladder.
The two prominent lines which form the sides of the trigone raaicid°, according to Sir C. Bell, are distinct muscles, the muscles of the ureters. They have their fixed point or origin at that prominence or tubercle existing at the inferior surface of the urethra, which has been already described as formed by the middle lobe of the prostate, their insertion or moveable point being at the opening of the ureters. Their use is to assist in the contractions of the bladder, to support and close the mouths of the ureters, and to preserve the obliquity of these muds by drawing them down during the contractions of the bladder. The tubercle whence these muscles are supposed to take their origin is termed the luctte or uvula veal= ; but these terms are more particularly applicable to it when enlarged and diseased. It then forma a prominent tumour at the orifice of the urethra, acts the part of a valve, and becomes a troublesome cause of retention of urine.
The arteries of the bladder are derived from the internal iliac and its branches: its veins entutv themselves into the internal iliac vein ; these vessels are most abun dant about its neck and bas fond. The lymphatics fol low the course of these ves sels. The nerves are of two kinds, the one derived from the sacral plexus of the cerebro-spinal system, the nerves of animal life ; the other derived from the hypogastric plexus of the sympathetic, the nerves of organic life.
The direction of the blad der is oblique, being inclined somewhat forwards and up wards. In proportion to the degree of distension the obliquity is increased, in consequence of the neck being fixed. It is retained in its position by two lateral ligaments, one on each side, and an anterior ligament ; the lateral ligaments are prolongations of the fascia iliaca, which passing down into the pelvis assumes the name of fascia pelvica, and becomes identified with the prostate gland and side of the bladder. The anterior ligament is double, and it isformed by the fascia transvergalis, which passing down behind the aymphyais pubis is reflected upon the upper surface of the prostate gland ; from the point of reflection two strong fasciculi of fibres pass to the anterior surface of the bladder. These ligaments are sometimes called the proper ligaments of the bladder to distinguish them from certain folds of the peritontrum, sometimes called false ligaments. the bladder is peculiarly interesting in a surgical point of view, anatomists have endeavoured to describe it precisely, and with this view they have divided it into six regions or surfaces—an anterior, a posterior, two lateral, a superior, and an inferior.