The bladder is situated in the pelvis (p. 63, and Fig. 157, p. 393), in front of the termination of the large bowel. Its front face is in contact with the inner surface of the junction of the pubic bones (sp., Fig. 24, p. 63); and when it is full the top of the bladder projects above the bone. It is in this position that pain is felt when the bladder is strained by overfulness. When full the bladder is pear-shaped, when empty it is collapsed and lies low in the pelvis. It consists of three coats, an outer fibrous layer, a middle of muscle, of the unstriped variety, whose fibres run in bundles forming an irre gular net-work, and an inner mucous layer with many layers of large epithelial cells on its surface. The peritoneum (p. 189) also in part organ. From the small end of the bladder a canal passes—the urethra,—into which the bladder opens, and by which it is put in communication with the outside. The narrow end is called the neck of the bladder, and is surrounded, at the junction with the urethra, by a special bundle of muscular fibres, called the sphincter of the bladder. Urine cannot escape from the bladder unless the guard of the sphincter is relaxed.
The functions of the bladder are to collect and retain the urine from the kidneys until a certain quantity accumulates, and then to expel it in a stream. The urine enters its receptacle from the ureters drop by drop, and when the bladder becomes distended its emptying is effected apparently by a reflex nervous act (p. 132). An impression passes to a centre low down in the spinal cord. An impulse is thus originated by which the sphincter muscle is relaxed and the muscular walls of the bladder caused to contract. The channel being open, the contraction of the walls exerts pressure on the contained fluid, which is thus expelled. Nervous diseases may affect the act of expul sion. The tone of the sphincter may be lost, so that the urine cannot be retained, or the bladder may be paralysed, so that the fluid cannot be driven out. Irritations may exist
about the neck of the bladder, or about the private parts, or due to worms in the bowel, which set up the reflex act and lead to a too frequent desire to empty the bladder. This is a frequent cause of children wetting their beds at night, the irritation originating the whole process, while the children are unconscious of it. Again, there may be some obstruction to the escape of the urine. Nevertheless, the pro cess being involuntary, the contractions of the bladder are set up, all the more vigorously since they are opposed, and thus the severe pain arises that is common in this condition. To this extent the action is voluntary, in that the result of the process may, for a time, be prevented by the will, or may be aided by voluntary effort producing contraction of the walls of the belly, and thus exerting pressure on the bladder.
The Prostate Gland.—In the male this is a glandular body which surrounds the urethra —the urinary outflow-tube--where it joins the bladder. It lies in the middle line behind the pubic bone, is cone-shaped with the point for ward, and is about lf inch long in the adult, 11 inch wide, and 1 inch thick. It consists of two lobes which meet and are continuous in the middle line. Its posterior surface rests on the front wall of the rectum— the end of the bowel. It is richly supplied with blood-vessels and nerves. Through the whole length of this structure the urinary canal passes before it opens in the bladder. Any overgrowth of this structure — hypertrophy,-- which is common after sixty years of age, or any tumour, may very seriously interfere with the calibre of the urinary canal passing through it, while any irritation or inflammation cannot fail to pro claim itself during the passing of water, and i during the emptying of the bowel.