The posterior surface is closely united to the vagina, in which the urethra is encased.
It is lined internally by mucous membrane, remarkable for three per manent and parallel longitudinal folds, and for numerous openings of mucous crypts. It has a layer of longitudinal fibres, and one of circular fibres, mingled with fibres of connective and lamellar tissue.
The ureters are two small conduits, which bring the urine from the kidneys to the bladder, and which open into the cavity of that organ at the superior angles of the trigonum vesicte.
The Rectum.
This is the terminal extremity of the large intestine, and the immediate prolongation of the sigmoid flexure of the colon, which occupies the left iliac fossa. Leaving the left sacroiliac synchondrosis it passes to the right, descends in front of the sacrum, which it reaches at the level of the third sacral vertebra, reaches the extremity of the coccyx, whence it passes downward and forward, then turns sharply backward to cross the perineal floor where it ends in the anus.
It has an anterior and a posterior surface.
The anterior surface is close to the uterus above, and the vagina below, uniting with this latter organ to form the recto-vaginal fold.
The posterior surface is next to the sacrum and coccyx, to which it is united by a fold of the peritoneum which forms the meso-rectum.
At its extremity the rectum is surrounded by the superior pelvic aponeurosis, the levator ani, the sphincter, a large vascular plexus, and the cellular tissue of the ischio-rectal cavity, which we have described above.
The internal surface of the rectum shows longitudinal folds, the columns of the rectum, and semi-circular folds. Its cavity, very narrow at its
superior portion, widens below and forms the ampulla of the rectum.
Structure. —A peritoneal coat, which forms the meso-rectum.
A muscular layer, formed of two fibrous layers, one with longitudinal fibres, the oiler with circular fibres. Some of these latter often form a circular ring 2 to 3 inches above the anus, called by Nelaton, the internal sphincter ani.
The mucous membrane is closely united to the muscularis in the upper portion of the rectum; it is, on the contrary, very loosely attached to the lower portion, especially in the child, whence the frequency of prolapsus of the mucous membrane in the latter. Below the internal sphincter are curvilinear folds, called semi-lunar valves. They enclose large tubular glands.
Vessels and arteries come from the inferior mesenteric, the hypogastric, and the internal pudic.
The veins form a true plexus, the hemorrhoidal plexus. They empty into the inferior mesenteric and hypogastric veins.
The lymphatics go to the lumbar glands.
The nerves come from the hypogastric and sacral plexus.
The rectum terminates in the anus. The anus is situated 1 inch in front of the apex of the coccyx. At the periphery, where the rectal mu cous membrane unites with the skin, it shows a series of folds which disappear by distention. It forms a true canal composed of two portions, one mucous, to which the internal sphincter is joined, the other cutaneous, to which the external sphincter is joined.