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The uterus (Figs. 91161, 91165, 91166) is a hollow, thick-walled, muscular organ situated deeply in the pelvic cavity between the bladder and rectum. Into its upper part the uterine tubes open, one on either side, while below, its cavity communicates with that of the vagina. When the ova are discharged from the ovaries they are carried to the uterine cavity through the uterine tubes. If an ovum be fertilized it imbeds itself in the uterine wall and is normally retained in the uterus until prenatal development is completed, the uterus undergoing changes in size and structure to accommodate itself to the needs of the growing embryo (see page 59). After parturition the uterus returns almost to its former condition, but certain traces of its enlargement remains. It is necessary, therefore, to describe as the type-form the adult virgin uterus, and then to consider the modifications which are effected as a result of pregnancy.
|In the virgin state the uterus is flattened antero-posteriorly and is pyriform in shape, with the apex directed downward and backward. It lies between the bladder in front and the pelvic or sigmoid colon and rectum behind, and is completely within the pelvis, so that its base is below the level of the superior pelvic aperture. Its upper part is suspended by the broad and the round ligaments, while its lower portion is imbedded in the fibrous tissue of the pelvis.||The long axis of the uterus usually lies approximately in the axis of the superior pelvic aperture, but as the organ is freely movable its position varies with the state of distension of the bladder and rectum. Except when much displaced by a fully distended bladder, it forms a forward angle with the vagina, since the axis of the vagina corresponds to the axes of the cavity and inferior aperture of the pelvis.||The uterus measures about 7.5 cm. in length, 5 cm. in breadth, at its upper part, and nearly 2.5 cm. in thickness; it weighs from 30 to 40 gm. It is divisible into two portions. On the surface, about midway between the apex and base, is a slight constriction, known as the isthmus, and corresponding to this in the interior is a narrowing of the uterine cavity, the internal orifice of the uterus. The portion above the isthmus is termed the body, and that below, the cervix. The part of the body which lies above a plane passing through the points of entrance of the uterine tubes is known as the fundus.||Body (corpus uteri).The body gradually narrows from the fundus to the isthmus.||The vesical or anterior surface (facies vesicalis) is flattened and covered by peritoneum, which is reflected on to the bladder to form the vesicouterine excavation. The surface lies in apposition with the bladder.||The intestinal or posterior surface (facies intestinalis) is convex transversely and is covered by peritoneum, which is continued down on to the cervix and vagina. It is in relation with the sigmoid colon, from which it is usually separated by some coils of small intestine.||The fundus (fundus uteri) is convex in all directions, and covered by peritoneum continuous with that on the vesical and intestinal surfaces. On it rest some coils of small intestine, and occasionally the distended sigmoid colon.||The lateral margins (margo lateralis) are slightly convex. At the upper end of each the uterine tube pierces the uterine wall. Below and in front of this point the round ligament of the uterus is fixed, while behind it is the attachment of the ligament of the ovary. These three structures lie within a fold of peritoneum which is reflected from the margin of the uterus to the wall of the pelvis, and is named the broad ligament.||Cervix (cervix uteri; neck).The cervix is the lower constricted segment of the uterus. It is somewhat conical in shape, with its truncated apex directed downward and backward, but is slightly wider in the middle than either above or below. Owing to its relationships, it is less freely movable than the body, so that the latter may bend on it. The long axis of the cervix is therefore seldom in the same straight line as the long axis of the body. The long axis of the uterus as a whole presents the form of a curved line with its concavity forward, or in extreme cases may present an angular bend at the region of the isthmus.||The cervix projects through the anterior wall of the vagina, which divides it into an upper, supravaginal portion, and a lower, vaginal portion.||The supravaginal portion (portio supravaginalis [cervicis]) is separated in front from the bladder by fibrous tissue (parametrium), which extends also on to its sides and lateralward between the layers of the broad ligaments. The uterine arteries reach the margins of the cervix in this fibrous tissue, while on either side the ureter runs downward and forward in it at a distance of about 2 cm. from the cervix. Posteriorly, the supravaginal cervix is covered by peritoneum, which is prolonged below on to the posterior vaginal wall, when it is reflected on to the rectum, forming the rectouterine excavation. It is in relation with the rectum, from which it may be separated by coils of small intestine.||The vaginal portion (portio vaginalis [cervicis]) of the cervix projects free into the anterior wall of the vagina between the anterior and posterior fornices. On its rounded extremity is a small, depressed, somewhat circular aperture, the external orifice of the uterus, through which the cavity of the cervix communicates with that of the vagina. The external orifice is bounded by two lips, an anterior and a posterior, of which the anterior is the shorter and thicker, although, on account of the slope of the cervix, it projects lower than the posterior. Normally, both lips are in contact with the posterior vaginal wall.||Interior of the Uterus (Fig. 91167).The cavity of the uterus is small in comparison with the size of the organ.||The Cavity of the Body (cavum uteri) is a mere slit, flattened antero-posteriorly. It is triangular in shape, the base being formed by the internal surface of the fundus between the orifices of the uterine tubes, the apex by the internal orifice of the uterus through which the cavity of the body communicates with the canal of the cervix.||The Canal of the Cervix (canalis cervicis uteri) is somewhat fusiform, flattened from before backward, and broader at the middle than at either extremity. It communicates above through the internal orifice with the cavity of the body, and below through the external orifice with the vaginal cavity. The wall of the canal presents an anterior and a posterior longitudinal ridge, from each of which proceed a number of small oblique columns, the palmate folds, giving the appearance of branches from the stem of a tree; to this arrangement the name arbor vitæ uterina is applied. The folds on the two walls are not exactly opposed, but fit between one another so as to close the cervical canal.||The total length of the uterine cavity from the external orifice to the fundus is about 6.25 cm.||Ligaments.The ligaments of the uterus are eight in number: one anterior; one posterior; two lateral or broad; two uterosacral; and two round ligaments.||The anterior ligament consists of the vesicouterine fold of peritoneum, which is reflected on to the bladder from the front of the uterus, at the junction of the cervix and body.||The posterior ligament consists of the rectovaginal fold of peritoneum, which is reflected from the back of the posterior fornix of the vagina on to the front of the rectum. It forms the bottom of a deep pouch called the rectouterine excavation, which is bounded in front by the posterior wall of the uterus, the supravaginal cervix, and the posterior fornix of the vagina; behind, by the rectum; and laterally by two crescentic folds of peritoneum which pass backward from the cervix uteri on either side of the rectum to the posterior wall of the pelvis. These folds are named the sacrogenital or rectouterine folds. They contain a considerable amount of fibrous tissue and non-striped muscular fibers which are attached to the front of the sacrum and constitute the uterosacral ligaments.||The two lateral or broad ligaments (ligamentum latum uteri) pass from the sides of the uterus to the lateral walls of the pelvis. Together with the uterus they form a septum across the female pelvis, dividing that cavity into two portions. In the anterior part is contained the bladder; in the posterior part the rectum, and in certain conditions some coils of the small intestine and a part of the sigmoid colon. Between the two layers of each broad ligament are contained: (1) the uterine tube superiorly; (2) the round ligament of the uterus; (3) the ovary and its ligament; (4) the epoöphoron and paroöphoron; (5) connective tissue; (6) unstriped muscular fibers; and (7) bloodvessels and nerves. The portion of the broad ligament which stretches from the uterine tube to the level of the ovary is known by the name of the mesosalpinx. Between the fimbriated extremity of the tube and the lower attachment of the broad ligament is a concave rounded margin, called the infundibulopelvic ligament.||The round ligaments (ligamentum teres uteri) are two flattened bands between 10 and 12 cm. in length, situated between the layers of the broad ligament in front of and below the uterine tubes. Commencing on either side at the lateral angle of the uterus, this ligament is directed forward, upward, and lateralward over the external iliac vessels. It then passes through the abdominal inguinal ring and along the inguinal canal to the labium majus, in which it becomes lost. The round ligaments consists principally of muscular tissue, prolonged from the uterus; also of some fibrous and areolar tissue, besides bloodvessels, lymphatics; and nerves, enclosed in a duplicature of peritoneum, which, in the fetus, is prolonged in the form of a tubular process for a short distance into the inguinal canal. This process is called the canal of Nuck. It is generally obliterated in the adult, but sometimes remains pervious even in advanced life. It is analogous to the saccus vaginalis, which precedes the descent of the testis.||In addition to the ligaments just described, there is a band named the ligamentum transversalis colli (Mackenrodt) on either side of the cervix uteri. It is attached to the side of the cervix uteri and to the vault and lateral fornix of the vagina, and is continuous externally with the fibrous tissue which surrounds the pelvic bloodvessels.||The form, size, and situation of the uterus vary at different periods of life and under different circumstances.||In the fetus the uterus is contained in the abdominal cavity, projecting beyond the superior aperture of the pelvis (Fig. 91168). The cervix is considerably larger than the body.||At puberty the uterus is pyriform in shape, and weighs from 14 to 17 gm. It has descended into the pelvis, the fundus being just below the level of the superior aperture of this cavity. The palmate folds are distinct, and extend to the upper part of the cavity of the organ.||The position of the uterus in the adult is liable to considerable variation, depending chiefly on the condition of the bladder and rectum. When the bladder is empty the entire uterus is directed forward, and is at the same time bent on itself at the junction of the body and cervix, so that the body lies upon the bladder. As the latter fills, the uterus gradually becomes more and more erect, until with a fully distended bladder the fundus may be directed backward toward the sacrum.||During menstruation the organ is enlarged, more vascular, and its surfaces rounder; the external orifice is rounded, its labia swollen, and the lining membrane of the body thickened, softer, and of a darker color. According to Sir J. Williams, at each recurrence of menstruation, a molecular disintegration of the mucous membrane takes place, which leads to its complete removal, only the bases of the glands imbedded in the muscle being left. At the cessation of menstruation, a fresh mucous membrane is formed by a proliferation of the remaining structures.||During pregnancy the uterus becomes enormously enlarged, and in the eighth month reaches the epigastric region. The increase in size is partly due to growth of preëxisting muscle, and partly to development of new fibers.||After parturition the uterus nearly regains its usual size, weighing about 42 gm.; but its cavity is larger than in the virgin state, its vessels are tortuous, and its muscular layers are more defined; the external orifice is more marked, and its edges present one or more fissures.||In old age the uterus becomes atrophied, and paler and denser in texture; a more distinct constriction separates the body and cervix. The internal orifice is frequently, and the external orifice occasionally, obliterated, while the lips almost entirely disappear.||Structure.The uterus is composed of three coats: an external or serous, a middle or muscular, and an internal or mucous.||The serous coat (tunica serosa) is derived from the peritoneum; it invests the fundus and the whole of the intestinal surface of the uterus; but covers the vesical surface only as far as the junction of the body and cervix. In the lower fourth of the intestinal surface the peritoneum, though covering the uterus, is not closely connected with it, being separated from it by a layer of loose cellular tissue and some large veins.||The muscular coat (tunica muscularis) forms the chief bulk of the substance of the uterus. In the virgin it is dense, firm, of a grayish color, and cuts almost like cartilage. It is thick opposite the middle of the body and fundus, and thin at the orifices of the uterine tubes. It consists of bundles of unstriped muscular fibers, disposed in layers, intermixed with areolar tissue, bloodvessels, lymphatic vessels, and nerves. The layers are three in number: external, middle, and internal. The external and middle layers constitute the muscular coat proper, while the inner layer is a greatly hypertrophied muscularis mucosæ. During pregnancy the muscular tissue becomes more prominently developed, the fibers being greatly enlarged.||The external layer, placed beneath the peritoneum, is disposed as a thin plane on the vesical and intestinal surfaces. It consists of fibers which pass transversely across the fundus, and, converging at each lateral angle of the uterus, are continued on to the uterine tube, the round ligament, and the ligament of the ovary: some passing at each side into the broad ligament, and others running backward from the cervix into the sacrouterine ligaments. The middle layer of fibers presents no regularity in its arrangement, being disposed longitudinally, obliquely, and transversely. It contains more bloodvessels than either of the other two layers. The internal or deep layer consists of circular fibers arranged in the form of two hollow cones, the apices of which surround the orifices of the uterine tubes, their bases intermingling with one another on the middle of the body of the uterus. At the internal orifice these circular fibers form a distinct sphincter.||The mucous membrane (tunica mucosa) (Fig. 91169) is smooth, and closely adherent to the subjacent tissue. It is continuous through the fimbriated extremity of the uterine tubes, with the peritoneum; and, through the external uterine orifice, with the lining of the vagina.||In the body of the uterus the mucous membrane is smooth, soft, of a pale red color, lined by columnar ciliated epithelium, and presents, when viewed with a lens, the orifices of numerous tubular follicles, arranged perpendicularly to the surface. The structure of the corium differs from that of ordinary mucous membranes, and consists of an embryonic nucleated and highly cellular form of connective tissue in which run numerous large lymphatics. In it are the tube-like uterine glands, lined by ciliated columnar epithelium. They are of small size in the unimpregnated uterus, but shortly after impregnation become enlarged and elongated, presenting a contorted or waved appearance (see page 60).||In the cervix the mucous membrane is sharply differentiated from that of the uterine cavity. It is thrown into numerous oblique ridges, which diverge from an anterior and posterior longitudinal raphé. In the upper two-thirds of the canal, the mucous membrane is provided with numerous deep glandular follicles, which secrete a clear viscid alkaline mucus; and, in addition, extending through the whole length of the canal is a variable number of little cysts, presumably follicles which have become occluded and distended with retained secretion. They are called the ovula Nabothi. The mucous membrane covering the lower half of the cervical canal presents numerous papillæ. The epithelium of the upper two-thirds is cylindrical and ciliated, but below this it loses its cilia, and gradually changes to stratified squamous epithelium close to the external orifice. On the vaginal surface of the cervix the epithelium is similar to that lining the vagina, viz., stratified squamous.||Vessels and Nerves.The arteries of the uterus are the uterine, from the hypogastric; and the ovarian, from the abdominal aorta (Fig. 91170). They are remarkable for their tortuous course in the substance of the organ, and for their frequent anastomoses. The termination of the ovarian artery meets that of the uterine artery, and forms an anastomotic trunk from which branches are given off to supply the uterus, their disposition being circular. The veins are of large size, and correspond with the arteries. They end in the uterine plexuses. In the impregnated uterus the arteries carry the blood to, and the veins convey it away from, the intervillous space of the placenta (see page 63). The lymphatics are described on page 714. The nerves are derived from the hypogastric and ovarian plexuses, and from the third and fourth sacral nerves.|