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Cavum Uteri. In comparison with the size of the organ, the cavity of the uterus is of small size owing to the great thickness of the uterine wall. In the body, the cavity is merely a narrow chink between the anterior and posterior walls, which are almost in contact (Fig. 1033). When, however, the uterus is opened from above downwards in frontal section of the organ, the cavity of the body has a triangular outline (Fig. 1032). The base of the triangle is directed upwards, and corresponds to a line drawn between the openings of the uterine tubes, while the apex is directed downwards towards the cervix. The sides of the triangle are convex inwards towards the cavity. The cavity of the body becomes continuous with that of the cervix by an opening called the orificium internum uteri (O.T. internal os uteri), which is a little smaller and more circular than the external orifice of the uterus. The cavity of the cervix, canalis cervicis uteri, or cervical canal, extends from the internal orifice of the uterus, where it joins the cavity of the body, to the external orifice, where it opens into the vagina. It is a somewhat spindle-shaped passage, which is narrower above and below than in its middle part; sections show also that its antero-posterior diameter is shorter than its transverse one, owing to an approximation of its anterior and posterior walls. In the body of
FIG. 1032.-A. THE POSTERIOR ASPECT OF THE UTERUS AND BROAD LIGAMENT (the broad ligament has
been spread out).
a, b, and c, the isthmus tube, the ligament of the ovary, and the round ligament of the right side cut short. B. DIAGRAMMATIC REPRESENTATION OF THE UTERINE CAVITY OPENED UP FROM ITS ANTERIOR ASPECT.
the uterus the walls of the cavity are smooth and even, but in the cervical canal the mucous membrane forms a remarkable series of folds, called the plica palmatæ (O.T. arbor vitæ uteri). These consist of an anterior and a posterior longitudinally directed fold or ridge, from which a large number of secondary folds, or ruge, branch off obliquely upwards and laterally (Fig. 1032, B).
Connexions of the Uterus and its Relations to the Peritoneum.-In addition to the uterine tubes at its upper lateral angles, and the vagina below, the uterus possesses other important connexions. Some of these are simply peritoneal folds passing from the uterus to neighbouring structures; others contain fibrous connective tissue, or smooth muscle fibres.
The peritoneum covering the fundus of the uterus is continued down over the vesical surface as far as the junction of the body and cervix, where it leaves the uterus to be reflected on to the bladder, forming the utero-vesical fold, or "anterior ligament of the uterus." The peritoneal recess between the bladder and the uterus is called the excavatio vesicouterina, or utero-vesical pouch. Below the level of this pouch the anterior aspect of the cervix is connected by loose tissue with the posterior, or basal, part of the bladder. Posteriorly the peritoneum covers the whole of the uterus, except the small portion of the cervix which projects into the upper part of the vagina. The peritoneum covering the intestinal surface of the uterus is continued to such a depth that it invests a small portion of the upper part of the posterior wall of the vagina before it is reflected on to the rectum, to form the recto-vaginal fold (Fig. 1033). The deep pouch between the uterus and
vagina in front and the rectum behind is called the excavatio rectouterina, or rectouterine pouch of Douglas, and its entrance is bounded on each side by a crescentic peritoneal fold, which passes from the posterior surface of the cervix uteri to the posterior wall of the pelvis, and ends near the side of the rectum. These crescentic folds are called the plicæ rectouterinæ, or recto-uterine folds of Douglas, and each contains between its layers a considerable amount of fibrous and smooth muscular tissue. A few of these fibres, which are continuous with the uterine wall, pass backwards to reach the rectum and constitute the musculus rectouterinus; others are said to gain an attachment to the front of the sacrum, and form a utero-sacral ligament. In many cases the recto-uterine folds become continuous with one another across the median plane behind the cervix uteri, and form, in this position, a transverse ridge termed the torus uterinus. The recto-uterine pouch of the female represents the recto-vesical pouch of the male, and the folds which bound it on each side, namely, the recto-uterine folds, correspond to the sacro-genital folds (sometimes called posterior false ligaments of the bladder) in the male sex.
The peritoneum of the vesical and intestinal surfaces, leaving the uterus along each lateral border to reach the side wall of the pelvis, forms the broad ligament of the uterus.
The ligamentum latum uteri, or broad ligament, is a wide peritoneal fold which passes from the lateral border of the uterus to the pelvic wall, and contains between its layers several important structures (Fig. 1032). The plane of the medial part of the ligament is determined by the position of the uterus. When the uterus is normally placed, the ligament has an anterior surface which looks downwards as well as forwards, and a posterior one which looks upwards and backwards. Near its attachment to the pelvis the ligament is placed more vertically. The free edge of the ligament contains the uterine tube, and follows the course pursued by that structure. Thus, in the undisturbed condition of parts, it at first passes horizontally laterally towards the uterine extremity of the ovary, where it ascends to arch over the tubal pole of the ovary on its medial side. Owing to the course pursued by the uterine tube round the ovary, the broad ligament forms a kind of curtain over the gland, and the ovary lies in a little pocket formed by the broad ligament, to which the name of bursa ovarica is applied (Figs. 1028 and 1029). This bursa ovarica is not to be confused with the fossa ovarii, or depression on the side wall of the pelvis, against which the ovary is usually placed.
The various structures in connexion with the broad ligament are most easily demonstrated when the ligament is spread out as flat as possible.
The ovary is connected with the posterior layer of the broad ligament by a very short mesentery, called the mesovarium, which, passing to the hilum, encloses the ovarian vessels and nerves as they reach the ovary. The part of the broad ligament which slings the uterine tube is called the mesosalpinx. When the ligament is spread out, the mesosalpinx has the form of a narrow triangle, the apex of which is at the lateral angle of the uterus, while the upper side is formed by the uterine tube, and the inferior one by the ligament of the ovary and the ovary itself. The narrow base of the triangle is directed laterally. Between the layers of this part of the broad ligament are situated the ep-oöphoron (O.T. parovarium), and the par-oöphoron (Fig. 1032). The part of the broad ligament below the level of the mesosalpinx is termed the mesometrium, and contains, especially in its lower part, a considerable amount of fatty connective tissue, the parametrium, and unstriped muscle fibres. The ureter and the uterine vessels lie in the lowest part of the broad ligament where it joins the pelvic floor. The fibrous and smooth muscle tissue which lies in the lower part of the broad ligament, immediately below the uterine artery, forms what is known as the lateral cervical ligament of the uterus. It is continuous with the dense tissue surrounding the branches of the hypogastric artery, and in vertical antero-posterior section has a triangular outline near its attachment to the cervix uteri.
The highest part of the attached lateral portion of the broad ligament forms the ligamentum suspensorium ovarii or suspensory ligament of the ovary, and contains between its layers the ovarian vessels and nerves as they enter or leave the pelvis.
The ligamentum ovarii proprium, or ligament of the ovary, is a rounded fibrous
cord, of about one inch in length, which is attached by its lateral end to the terine pole of the ovary, and by its medial end to the lateral angle of the uterus immediately below and behind the entrance of the uterine tube. This ligament, which is largely composed of unstriped muscle fibres continuous with those of the uterus, is enclosed in a slight fold derived from the posterior layer of the broad ligament.
The ligament of the ovary represents the upper portion of the gubernaculum which appears in the embryo.
The ligamentum teres uteri, or round ligament of the uterus, is a narrow flat band attached to the uterus just in front of, and a little below, the opening of the uterine tube. Near the uterus it contains numerous smooth muscle fibres, which are continuous with those of the uterus; more laterally it is composed chiefly of fibrous connective tissue. Lying in the anterior part of the broad ligament, it reaches the wall of the pelvis minor, and is then directed forwards and slightly upwards to cross the obliterated umbilical artery and the pelvic brim. After it has reached the pelvic wall its course is comparable to that of the ductus deferens in the male, and, like the latter, it leaves the abdomen to traverse the inguinal canal (Figs. 1028 and 1029). It finally ends in the subcutaneous tissue and skin of the labium majus. Its terminal part is composed of connective tissue only.
In some cases a small diverticulum of the peritoneal cavity can be traced accompanying the round ligament through the abdominal wall. This is called the processus vaginalis peritonei (O.T. canal of Nuck), and corresponds to the processus vaginalis of the male (p. 1294).
The round ligament of the uterus represents the lower portion of the gubernaculum testis which appears in the male embryo (see pp. 1294 and 1313).
Position and Relations of the Uterus.-The position occupied by the uterus in the pelvis is not always the same, but varies with the conditions of the neighbouring organs. The lower cervical part is, however, much more firmly fixed in place than the body and fundus, which possess a considerable amount of mobility. Usually the level of the external orifice of the uterus will be found to correspond to that of a horizontal plane passing through the upper margin of the symphysis. pubis. The uterus rarely lies exactly in the median plane of the body, but usually bends to one or other side, most frequently towards the right. The vesical surface of the uterus rests against the bladder, and follows the rising or falling of its superior wall as that organ becomes filled or emptied. When the bladder is empty the long axis of the uterus points forwards and upwards, and the organ is said to be in an anteverted position. Also, the long axis of the uterus is bent on itself where the body joins the cervix, and so the organ is said to be anteflexed. The anteflexion is due to the fact that the more rigid cervix is fixed, while the movable upper part of the uterus sinks forwards, following the bladder wall. With the empty condition of the bladder the angle formed between the long axis of the uterus and that of the vagina is about a right angle. When the bladder becomes filled, the anteversion and anteflexion of the uterus become less marked, owing to the body and fundus being pushed backwards. Finally, if the rectum is empty and the bladder very much distended, the uterus is pushed so much backwards that the long axis of the organ may nearly correspond to that of the vagina. The uterus is then said to be retroverted. Superiorly a part of the peritoneal cavity intervenes between the vesical surface of the uterus and the bladder, but lower down the two organs are separated merely by a small quantity of connective tissue. The intestinal surface of the uterus looks into the pouch of Douglas, and is usually, like the fundus, in relation to some loops of the small intestine or pelvic colon. Laterally the uterus is related to the broad ligaments. The terminal parts of the ureters pass downwards, medially, and a little forwards on the lateral aspects of the cervix, but are separated from it by an interval of about three-quarters of an inch. The lowest part of the cervix is, as we have seen, enclosed within the cavity of the vagina.
On each side of the cervix uteri and upper part of the vagina there is an interval in which lie numerous large vessels. These are surrounded by loose fatty tissue, which is continued upwards for a considerable distance between the layers of the broad ligament. This loose tissue, which is of surgical importance, has received the name parametrium. ̧
Structure of the Uterus.-The thick uterine wall is composed of three chief layers, which are termed respectively the serous, the muscular, and the mucous coats.
Tunica Serosa. The serous coat, or perimetrium, is derived from the peritoneum, and covers the whole organ except the part of the cervix which projects into the vagina and the anterior surface of its supra-vaginal portion. At the borders it is continued into the broad ligaments. Over the fundus and body of the uterus the serous coa! is very firmly adherent to the deeper layers, and cannot be easily peeled off withou: tearing either it or the underlying muscular tissue. Near the borders the peritoneum is less firmly attached, and over the posterior aspect of the cervix it may readily be stripped off without injury to the underlying structures.
Tunica Muscularis.-The muscular coat is composed of unstriped fibres, and forms the chief part of the uterine wall. Inferiorly the muscular coat of the uterus becomes continuous with that of the vagina. The more superficial layer of the muscular coat sends prolongations into the recto-uterine folds, into the round and broad ligaments of the uterus, and into the ovarian ligaments. Other fibres join the walls of the uterine tubes. The main branches of the blood-vessels and nerves of the uterus lie among the muscle fibres. In the deeper layers of the muscular coat a considerable amount of connective tissue and some elastic fibres are to be found. The muscular coat of the cervix, or tunica muscularis cervicis, contains more connective and elastic tissue than that of the body, and hence the greater firmness and rigidity of the cervical part of the uterus.
The deeper and thicker part of the muscular tissue of the uterus is considered by some anatomists to represent a muscularis mucosa, and is therefore described as part of the mucous coat. The deep and superficial portions of the muscular coat are, however, quite continuous, and there is no representative of a submucous vascular layer of tissue such as in the alimentary canal separates the muscular coat from the muscularis mucosa. In the uterus the blood-vessels lie in the muscular coat.
Tunica Mucosa.-The mucous coat in the body of the uterus is smooth and soft, and covered with columnar ciliated epithelium. Simple tubular glands, glandulæ uterinæ, also lined with a ciliated epithelium, are present in the mucous membrane, and penetrate in their deeper parts into the muscular coat. In the cervix of the uterus the mucous coat is firmer and more fibrous than in the body, and its surface is not smooth, but presents a number of peculiarly disposed ridges which have been already described. Like the mucous membrane of the body of the uterus, that of the cervix is covered with a ciliated epithelium which passes into squamous epithelium just inside the external orifice of the uterus. The cervix uteri possesses, in addition to unbranched tubular glands, resembling those present in the body, numerous somewhat branched glands, the glandulæ cervicales uteri. Both kinds of glands are lined by ciliated epithelium. In many cases little clear retention cysts, "ovules of Naboth," are to be seen in the cervical mucous membrane. These arise as a result of obstruction at the mouths of the glands.
Differences in the Uterus at Different Ages.-At birth the cervix uteri is relatively larger than in the adult organ, and its cavity is not distinctly marked off from the interior of the body by an internal orifice. At this time also the plicæ palmatæ extend throughout the whole length of the uterus. The organ grows slowly until just before puberty, when its growth is rapid for a time. As the body of the uterus increases in size the mucous membrane becomes smooth and the plica palmatæ become restricted to the cervix. In women who have borne children the cavity remains permanently somewhat wider and larger than in cases where the uterus has never been pregnant.
In old age the uterine wall becomes harder and has a paler colour than it possesses in the young subject.
Variations. In rare cases the uterus may be divided by a septum into two distinct cavities, or its lateral angles may be produced into straight or curved processes, called "horns" or cornus. The latter abnormality recalls the appearance of the bicornuate uteri of some animals. Both the above conditions arise from an arrest in the fusion of the two separate tubes--the Mullerian ducts-which normally unite in the embryo to form the uterus.
Periodic Changes in the Uterine Wall.-At each menstrual period a remarkable series of changes occurs which results in a periodic shedding of the superficial parts of the uterine mucous membrane. For a few days before menstruation begins, the mucous membrane gradually thickens and becomes more vascular, while at the same time its surface becomes uneven. Soon the superficial parts of the
mucous membrane disintegrate and hæmorrhage takes place from the small superficial blood-vessels. In this way a hæmorrhagic discharge is caused, and the superficial parts of the uterine mucous membrane are shed at each period. When menstruation is over the mucous membrane is rapidly regenerated.
Pregnant Uterus.-The pregnant uterus increases rapidly in size and weight, so that from being three inches in length and one, ounce in weight, it becomes by the eighth month about seven or eight inches in length and sometimes as much as two pounds in weight. In shape the uterus is now oval or rounded, with a thick wall composed chiefly of muscle fibres arranged in distinct layers. The rounded fundus is very prominent. The round ligaments are stronger and better marked, and the layers of the broad ligament become separated in their medial parts by the growth of the uterus between them. The blood-vessels, especially the arteries, are very large and tortuous. The changes which occur in the mucous membrane of the pregnant uterus are intimately connected with the manner in which the developing foetus receives its nutrition, and have been noticed on pp. 56 et seq.
Vessels and Nerves of the Uterus.-The uterus receives its arterial supply mainly from the uterine arteries, which are branches of the hypogastric arteries, and also from the ovarian arteries, branches of the aorta. The vessels derived from these two sources communicate freely with one another. Each uterine artery, reaching the side of the lower part of the uterus, divides into a large branch which passes upwards to supply the body and fundus, and a much smaller branch which passes downwards to supply the cervix. The vessels distributed to the body and fundus have an exceedingly tortuous course. The branches of the uterine artery, having entered the muscular coat, break up within its deeper layers into smaller twigs which supply the muscular tissue and the mucous coat. The small uterine branch from the ovarian artery reaches the uterus in the region of the lateral angle. During pregnancy the arteries become enormously enlarged.
The thin-walled veins form a plexus which pours its blood into the tributaries of the hypogastric vein.
The nerves of the uterus are derived chiefly from a plexus placed in the neighbourhood of the cervix uteri, to which the term plexus uterovaginalis or "cervical ganglion" is applied. Superiorly this plexus is continuous with the hypogastric plexus, but it also receives fibres from the third and fourth sacral nerves. In addition to fibres from the plexus uterovaginalis, the uterus receives fibres directly from the hypogastric plexus, and also from the plexus vesicalis.
Clinical observations indicate that afferent impulses reach the central nervous system from the uterus through the posterior roots of the tenth, eleventh, and twelfth thoracic nerves, the first lumbar, and the second, third, and fourth sacral nerves.
The numerous lymph-vessels coming from the body of the uterus join those from the ovary, and end for the most part in the lumbar lymph-glands. Along the course of the round ligament of the uterus there are a few lymph-vessels which establish a connexion between the lymph-network surrounding the uterus and the inguinal lymph-glands. The lymphvessels from the cervix uteri end in the gland placed near the bifurcation of the common iliac artery.
The vagina is a passage about three inches in length, open at its lower end, and communicating above with the cavity of the uterus. The passage is directed downwards and forwards, describing a slight curve which is convex backwards. The axis of the vagina forms with that of the uterus an angle which is open forwards. This angle is usually somewhat greater than a right angle, but varies with the condition of the neighbouring viscera (p. 1319). The vagina is widest at its upper end (Fig. 1034), and normally its anterior wall and its posterior wall are in contact. In transverse section the lower part is usually an H-shaped cleft, the middle part a simple transverse slit, while the lumen of the upper portion, into which the cervix uteri projects, is more open. The lower part of the cervix uteri has the appearance of entering the vagina through the upper portion of its anterior wall (Fig. 1033). As more of the posterior than of the anterior part of the cervix projects into the vagina, a deeper recess is formed between the vaginal wall and the cervix behind than in front or laterally. The term anterior fornix is often applied to the angle, or recess, in front; posterior fornix to the deeper angle behind, and lateral fornix to the recess on each side of the cervix uteri, between it and the wall of the vagina. The anterior wall of the vagina (paries anterior) is shorter than the posterior (paries posterior), the former being about three inches in length,