As pregnancy advances, the Fallopian tubes undergo other changes as respects their situation, which are worthy of notice. The broad ligaments, in the upper parts of which the Fallopian tubes take their course, are well known to be merely expansions of peritoneum from each side of the uterus, and therefore become gradually unfolded and shorter as the uterus increases in size. “In proportion as the fundus uteri rises upwards and increases in size, the upper part of the broad ligament is so stretched that it clings close to the side of the uterus, so that in reality the broad ligament disappears, no more of it remaining than its very root, viz. its upper and outer corner, where the group of spermatic vessels pass over the iliacs immediately to the side of the uterus. In this state, though the small end of the tube opens in the same part of the uterus as before impregnation, yet the tube has a very different direction. Instead of running outwards in the horizontal direction, it runs downwards, clinging to the side of the uterus. And behind the fimbriæ lies the ovarium, for the same reason clinging close to the side of the uterus.”[8]
Uterus. The uterus is a hollow fibrous viscus situated in the hypogastric region between the bladder and the rectum, below the intestinum ileum and above the vagina, and is by far the largest of the generative organs. It is of a pyriform figure: its upper portion which is the largest is triangular, becoming gradually smaller inferiorly; that portion of it which is above the spot where the Fallopian tubes enter is called the fundus uteri; the lower and cylindrical portion receives the name of cervix; that between the cervix and fundus is called the body of the uterus.
The parietes of the adult uterus are nearly half an inch in their greatest thickness, which is about the middle of the body, the body being slightly thicker than the cervix, which is of a somewhat harder structure. Near the point at which the Fallopian tubes enter the uterus the parietes become thinner, gradually diminishing from four or five to only one line in thickness.
The cavity of the uterus is triangular, its base being directed upwards, the superior angles corresponding to the points where the Fallopian tubes enter it. The cavity of the uterus is so small, owing to the thickness of its parietes, that they are nearly in contact: it is only four lines in breadth; the fundus, which forms the base of the triangle, is convex both internally as well as externally; whereas, the sides which form the body are convex internally, but somewhat concave externally.
The cavity of the uterus is most contracted at the point where the cervix is united to the body, which here forms the os uteri internum; from this point the cervix gradually dilates as far as its middle portion, when it again contracts; its lower extremity terminates in the upper part of the vagina by an anterior and posterior cushion-like projection, of which the posterior is usually the longest, although from the direction of the uterine axis the anterior is commonly felt lowest in the pelvis. Between these there is a transverse fissure known by the name of os tincæ or os uteri externum, the lips or labia of which are formed by the two above-mentioned prominences. The internal surface of the body of the uterus is smooth, whereas that of the cervix is uneven, forming upon its anterior and posterior wall a number of delicate rugæ diverging obliquely in an arborescent form, and hence called the arbor vitæ. The lips of the os uteri are smooth, except when slight lacerations have taken place during labour.
In the virgin state the uterus is about two inches long, of which the cervix occupies the smaller half: the greatest breadth of the body is sixteen lines; that of the cervix from nine to ten. The uterus which has been impregnated, especially when this has been frequently the case, scarcely ever regains its original dimensions, and the fissure which the os tincæ forms becomes broader from before backwards. The weight of an adult virgin uterus is from seven to eight drachms, but the uterus which has been once impregnated is seldom less than an ounce and a half. It lies between the bladder and rectum, its upper half being covered by peritoneum, which closely adheres to it. In the adult state it is situated entirely in the cavity of the pelvis; the fundus, which is below the upper edge of the symphysis pubis, is turned forwards and upwards, while its mouth is directed downwards and backwards, so that its long axis is nearly parallel to the axis of the superior aperture of the pelvis.
The uterus is connected to the neighbouring parts by several duplicatures of peritoneum, which are continuous with that portion of it which covers the fundus. The most considerable are the broad or lateral ligaments: these arise from the sides of the uterus, which is enclosed between their anterior and posterior layers or laminæ; they proceed transversely outwards towards the sides of the pelvic cavity, which is thus divided into two portions, and are then continued into that portion of the peritoneum which lines the cavity.
The round ligaments arise from the sides of the uterus close beneath and a little anterior to the uterine extremity of the Fallopian tubes. They pass between the two layers of the broad ligaments, behind the umbilical arteries, and before the iliac vessels, in a direction upwards and outwards to the external opening of the inguinal canal; they then make a turn round the epigastric artery downwards, inwards, and forwards, and pass through the abdominal ring, and dividing into numerous fasciculi and fibres are gradually lost in the cellular substance of the mons Veneris and upper portion of the labia. Besides consisting of cellular substance and blood-vessels, the round ligaments contain some very distinct bundles of muscular fibres, of which the upper arise from the external layer of uterine fibres, and the lower from the inferior edge of the internal oblique muscle, and pass upwards.
Upon a superficial examination, the structure of the uterus would almost seem to be homogeneous, nevertheless a number of reddish yellow strata interspersed with whitish streaks running from behind forwards may be perceived even in the unimpregnated state; between these strata the vessels of the uterus take their course, forming numerous anastomoses.
There is much difference of opinion among anatomists as to the fibrous structure of the uterus. The majority however agree as to the presence of muscular fibres,[9] some considering that they always exist, while others, and by far the greater number, consider them as appearances peculiar to pregnancy: they are, it is true, extremely indistinct in the unimpregnated state, but they are far from being peculiar to pregnancy, as they are frequently developed by any circumstances by which the formative powers of the uterus are excited. Thus in cases where the uterus has been much distended by some anormal growth, its fibres become much developed and distinctly fasciculated. Lobstein observed them very distinctly in a uterus which had been distended to the size of a seven months’ pregnancy by a fatty tumour.