The Urinary System.

The, organs of this system axe devoted to separating the urine from the blood, and carrying it out of the body. These organs are the kidneys, the ureters, the bladder and the urethra.

The Kidneys lie one on each side of the backbone, in the lumbar region, behind the peritoneum. They are four or five inches long, and two and a half broad. They are in shape Eke the kidneybean, and weigh about half a pound each. In the centre there is a bag called the pelvis, which tapers like a funnel, and unites with the ureter which conveys the urine to the bladder. The texture of the kidney is dense, presenting in its interior two structures, an external or cortical, and an internal or medullary. The cortical portion has the bloodvessels, the medullary is composed of tubes which carry away the urine.

The Ureters are membranous tubes of the size of a goosequill, and eighteen inches long, which run down the back wall of the abdomen, behind the peritoneum, to the bladder, into each side of which they empty their contents.

The Bladder is located in the pelvis, in front of the rectum. It is composed of three coats; the external is serous, the middle muscular, and the internal mucous. The external coat is strong and fibrous; the internal is drawn into wrinkles, which makes it thick and shaggy; it secretes a mucus which prevents it from being injured by the corrosiveness of the urine. The urine is retained in the bladder by means of a circular muscle, called a sphincter, which draws the mouth of the organ together. When the quantity of urine is so increased as to give some uneasiness or pain, this 3iausele, by a sort of instinct, relaxes and lets it out. The bladder is attached to the rectum, to the hipbones, to the peritoneum, and to the navel, by several ligaments. In the female the bladder has the womb between it and the rectum. This organ is wisely provided as a receptacle for the urine; which, without it, would produce a great inconvenience by being constantly dribbling away.

The Urethra is a membranous canal which leads from the neck of the bladder. It is composed of two layers, a mucous and an elastic fibrous. Through this channel, which is curved in its course, the urine passes out of the body.