=The Bladder and Urethra.=--In their course to the bladder the ureters pass from the abdominal into the pelvic cavity, but before describing the pelvis itself it will be well to complete the account of the urinary organs by considering the bladder and urethra. The _bladder_ is the reservoir for the urine and has muscular walls lined with mucous membrane. A peritoneal coat covers the upper surface and is reflected to the walls of the abdomen and pelvis. It is situated back of the os pubis, the front bone of the pelvis, with its base or fundus directed downward and backward. Normally it is in the pelvis, but when much distended it mounds up into the abdominal cavity, where it can be felt in front as a tumor. It rests on the rectum in the male and on the cervix in the female and is held in place by numerous ligaments. When empty it may be Y-shaped, but it becomes oval when distended. Its capacity is about one pint. The lower abdominal wall and the anterior wall of the bladder may be wanting congenitally. In paralysis of the sphincter at the neck of the bladder distention results. _Stones_ may be found in the bladder. From the neck of the bladder the urine passes out of the body through the _urethra_. This in the male passes down through the penis and is about ten inches long. Except when urine is passing it is a transverse slit with the upper and under surfaces in contact, while at the end of the penis the slit of the meatus urinarius is vertical. When the penis is flaccid, the urethra describes a sharp curve before its entrance into the bladder, but it becomes approximately straight when the penis is raised at right angles to the body--an important point to remember in catheterization. In the female the urethra is straight and much shorter, being only about one and a half inches long. The _meatus urinarius_ is in the anterior vaginal wall about one inch behind the clitoris. Sometimes the urethra is _ruptured_ in a fall. _Stricture_ of the urethra occurs sometimes after gonorrhoea, owing to the formation of scar tissue following ulcer. CHAPTER XI. THE PELVIS AND THE GENITAL ORGANS. =The Pelvis.=--Before taking up the pelvic organs, the pelvis itself should be described. The name pelvis has been given to the bony ring which is interposed between the spine and the femurs on account of its resemblance to a basin. At the back of this basin or pelvis are the _sacrum_ and _coccyx_, already described in connection with the back, and at the sides and meeting in the median line in front are the two _ossa innominata_ or _nameless bones_, so called on account of their peculiar and indescribable shape. At birth each os innominatum is made up of three bones, the _ilium_, _ischium_, and _pubes_, but about the age of puberty the three become welded into one. At their point of junction is the cavity of the acetabulum for articulation with the head of the femur or thigh bone.