THE VAGINA.
This is a membranous canal, leading from the vulva to the uterus, and corresponding in direction with the axis of the outlet of the pelvis. It is constricted at its commencement, but near the uterus becomes dilated, and is closed by the contact of the anterior with the posterior wall. Its length is variable; but it is always longer upon the posterior than upon the anterior wall, the former being usually about five or six inches in length, and the latter four or five. It is attached to the cervix of the uterus, which latter projects into the upper extremity of the canal.
In structure, the vagina is composed of a mucous lining, a layer of erectile tissue, and an external tunic of contractile fibrous tissue, resembling the dartos of the scrotum. The upper fourth of the posterior wall is covered, on its pelvic surface, by the peritoneum, while in front the peritoneum is reflected from the upper part of the cervix of the uterus to the posterior surface of the bladder. On each side it gives attachment, superiorly to the broad ligaments of the uterus, and inferiorly to the pelvic fascia and levatores ani.
The mucous membrane presents a number of transverse papillæ or rugæ, upon its upper and lower surfaces, which extend outward on each side from a middle raphé. The transverse papillæ and raphé are more apparent upon the upper than upon the lower surface, and the two raphé are called the columns of the vagina. The mucous membrane is covered by a thin cuticular epithelium, which is continued from the labia, and terminates by a fringed border at about the middle of the cervix uteri.
The middle, or erectile layer, consists of erectile tissue enclosed between two layers of fibrous membrane; this layer is thickest near the commencement of the vagina, and becomes gradually thinner as it approaches the uterus.
The external, or dartoid layer of the vagina, serves to connect it to the surrounding viscera. Thus it is very closely adherent to the under surface of the bladder, and drags that organ down with it in prolapsus uteri. To the rectum it is less closely connected, and that intestine is therefore less frequently affected in prolapsus.
The uterus is a flattened organ, of a pyriform shape, having the base directed upward and forward, and the apex downward and backward in the line of the axis of the inlet of the pelvis, and forming a considerable angle with the course of the vagina. It is convex on its posterior surface, and somewhat flattened upon its anterior aspect. In the unimpregnated state it is about three inches in length, two in breadth across its broadest part, and one in thickness, and is divided into fundus, body, cervix, and os uteri. At the period of puberty, the uterus weighs about one ounce and a half: after parturition, from two to three ounces; and at the ninth month of utero-gestation, from two to four pounds.
The fundus and body are inclosed in a duplicature of peritoneum, which is connected with the two sides of the pelvis, and forms a transverse septum between the bladder and rectum. The folds formed by this duplicature of peritoneum on either side of the organ are the broad ligaments of the uterus. The cervix is the lower portion of the organ; it is distinguished from the body by a well-marked constriction; to its upper part is attached the upper extremity of the vagina, and at its extremity is an opening, which is nearly round in the virgin, and transverse after parturition; the os uteri, bounded before and behind by two labia, the anterior labium being the most thick, and the posterior somewhat the longest. The opening of the os uteri is of considerable size, and is named the orificium uteri externum; the canal then becomes narrowed, and at the upper end of the cervix is constricted into a smaller opening, the orificium internum. At this point the canal of the cervix expands into the shallow triangular cavity of the uterus, the inferior angle corresponding with the orificium internum, and the two superior angles, which are funnel-shaped, and represent the original bicornute condition of the organ, with the commencement of the Fallopian tubes. In the canal of the cervix uteri are two or three longitudinal folds, to which numerous oblique folds converge, so as to give the idea of branches from the stem of a tree; hence this appearance has been denominated the arbor vitæ uterina. Between these folds, and around the os uteri, are numerous mucous follicles. It is the closure of the mouth of one of these follicles, and the subsequent distention of the follicle, with its proper secretion, that occasion those vesicular appearances so often noticed within the mouth and cervix of the uterus, called the ovula of Naboth.
Structure.—The uterus is composed of three tunices: of an external, or serous coat, derived from the peritoneum, which constitutes the duplicatures on each side of the organ, called the broad ligaments; of a middle, or muscular coat, which gives thickness and bulk to the uterus; and of an internal, or mucous membrane, which lines its interior, and is continuous, on the other hand, with the mucous lining of the Fallopian tubes, and on the other with that of the vagina. In the unimpregnated state, the muscular coat is exceedingly condensed in texture, offers considerable resistance to section with the scalpel, and appears to be composed of whitish fibers, inextricably interlaced and intermingled with blood-vessels. In the impregnated uterus the fibers are of large size, and distinct, and are disposed in two layers, superficial and deep. The superficial layer consists of fibers, which pursue a vertical direction, some being longitudinal and others oblique. The longitudinal fibers are found principally upon the middle line, forming a thin plane upon the anterior and posterior face of the organ, and upon its fundus. The oblique fibers occupy chiefly the sides and fundus. At the angles of the uterus, the fibers of the superficial layer are continued outward upon the Fallopian tubes, and into the round ligaments and ligaments of the ovaries. The deep layer consists of two hollow cones of circular fibers, having their apex at the openings of the Fallopian tubes, and by their bases intermingling with each other on the body of the organ. These fibers are continuous with the deep muscular layer of the Fallopian tubes, and indicate the primitive formation of the uterus by the blending of these two canals. Around the cervix uteri the muscular fibers assume a circular form, interlacing with and crossing each other at acute angles. The mucous membrane is provided with a columnar ciliated epithelium, which extends from the middle of the cervix uteri to the extremities of the Fallopian tubes.
Vessels and Nerves.—The arteries of the uterus are the uterine, from the internal iliac, and the spermatic, from the aorta. The veins are very large and remarkable; in the impregnated uterus they are called sinuses, and consist of canals, channeled through the substance of the organ, being merely lined by the internal membrane of the veins. They terminate on each side of the uterus in the uterine plexuses. The lymphatics terminate in the lumbar glands.
The nerves of the uterus are derived from the hypogastric and spermatic plexuses, and from the sacral plexus. They have been made the subject of special investigation by Dr. Robert Lee, who has successfully repaired the omission made by Dr. William Hunter, in this part of the anatomy of the organ. In his numerous dissections of the uterus, both in the unimpregnated and gravid state, Dr. Lee has made the discovery of several large nervous ganglia and plexuses. The principal of these, situated on each side of the cervix uteri, immediately behind the ureter, he terms the hypogastric ganglion; it receives the greater number of the nerves of the hypogastric and sacral plexus, and distributes branches to the uterus, vagina, bladder, and rectum. Of the branches to the uterus, a large fasciculus proceeds upward by the side of the organ, toward its angle, where they communicate with branches of the spermatic plexus, and form another large ganglion, which he designates the spermatic ganglion, and which supplies the fundus uteri. Besides these, Dr. Lee describes vesical and vagina ganglia, and interior and posterior subperitoneal ganglia, and plexuses, which communicate with the preceding, and constitute an extensive nervous rete over the entire uterus. Dr. Lee concludes his observations by remarking: “These dissections prove that the human uterus possesses a great system of nerves, which enlarges the coats, blood-vessels, and absorbents during pregnancy, which returns, after parturition, to its original condition before conception takes place. It is chiefly by the influence of these nerves that the uterus performs the varied functions of menstruation, conception, and parturition, and it is solely by their means that the whole fabric of the nervous system sympathizes with the different morbid affections of the uterus. If these nerves of the uterus could not be demonstrated, its physiology and pathology would be completely inexplicable.”