The uterus is a hollow, muscular, pear-shaped body, situated in the true pelvis. Its larger upper portion is termed the body or corpus uteri, and the smaller lower one the neck or cervix uteri, these two portions being separated by a constriction which is the narrowest part of the organ. The portion of the body which projects markedly above the entrances of the tubes is known as the fundus, and as the uterus is markedly flattened from before backward, an anterior and a posterior surface and two lateral margins may be recognized in it. The anterior surface is known as the vesical surface, the posterior more convex one as the intestinal surface, and the lateral margins as the right and the left. That portion of the cervix which projects into the vagina is termed the vaginal portion, while that situated above the vagina is called the supravaginal portion.

The thick uterine wall surrounds a relatively small cavity in the body of the organ termed the uterine cavity, and in the cervix known as the canal of the cervix. The junction of the two portions is at the internal os uteri, the narrowest portion of the uterine lumen, corresponding to the constriction between the body and the cervix. The uterine cavity is merely a capillary space anteroposteriorly, but it has some extent in the transverse direction. It is irregularly triangular in shape, one angle being at the internal os and the other two at the internal orifices of the tubae uterinae, the line connecting the latter points being the shortest side of the triangle.
The canal of the cervix is approximately cylindrical, being slightly dilated at its center; it begins at the internal os uteri and opens into the vagina through the external os uteri. The external os of a nullipara as seen from the vagina is either a short transverse slit with smooth margins or a smooth round opening; in women who have borne children it is irregularly circular and exhibits a number of notches. Its thick margins are termed the lips (labia), the anterior being shorter and at a lower level than the posterior one. They are covered by the smooth vaginal mucous membrane and form the vaginal portion of the cervix.
On account of its intimate connection with the vagina the cervix of the uterus may be regarded as stationary, while the body is movable. The position of the internal os ijteri is consequently on the line about which as about a transverse axis the body moves upon the cervix. The position of the uterus is essentially dependent upon the degree of distention of the bladder; when this viscus is empty, the uterine body is bent anteriorly upon the cervix (anteflexion) ; when it is full, the uterus straightens out so that the axes of the body and cervix more nearly correspond. In addition to this, the uterine axis is not placed vertically in the pelvic cavity, but passes obliquely from above downward and from before backward, so that the uterus seems " ante vert ed." These circumstances explain the varying levels of the lips of the external os. The uterus is not, as a rule, situated exactly in the median plane, but is inclined either to the right or to the left, so that the fundus is not directed exactly anterior but to one or the other side (sinistroversion, dextro- version).
The peritoneal covering of the uterus is derived from the broad ligaments, which approach its lateral margins; the peritoneum invests its entire posterior surface, the posterior lip of the external os, and also the posterior aspect of the upper portion of the vagina. Upon the anterior surface, however, the peritoneal coat extends only to the level of the internal os, so that it is only the uterine body which is completely enveloped, the entire anterior surface of the cervix being uncovered by peritoneum. The peritoneal coat of the vesical surface passes over the fundus to become continuous with that of the intestinal surface without demarcation.
The uterus is situated in the central portion of the true pelvis and its vesical surface is always in contact with the urinary bladder. The cervix is rather firmly connected with the posterior vesical wall, but the body is separated from the bladder by the vesico-uterine fold of peritoneum.
In the normal position of anteflexion this vesico-uterine pouch is a capillary space and never contains intestinal coils, so that the body of the uterus must follow the bladder in its varying degree of distention. The top of the uterine fundus extends upward to about the level of the transverse vesical fold. The intestinal surface of the uterus is usually in relation with the intestinal coils situated in the recto- uterine pouch, but when the bladder and rectum are full it is in contact with the anterior rectal wall.
The portion of the uterus uncovered by peritoneum exhibits the following relations. At the junction of the supravaginal and vaginal portions of the cervix the vaginal mucous membrane is inserted, the musculature of the vagina being directly continuous with that of the uterus. The relations of the vaginal portion of the cervix within the vagina will be considered later on; those of the supravaginal portion are largely dependent upon the nature of the fixation of this portion of the uterus, the anterior surface of the cervix being in relation with the posterior vesical wall and with the ureter, the latter structure being about one centimeter distant. The main vessels pass to the lateral margins of the uterus.
The size and shape of the uterus vary according to its age and function. The infantile uterus is proportionately very small and does not grow much until puberty, and, compared with the cervix, the body is very small, broad and flat. The virgin uterus and that of a nullipara is still relatively small and the body and the cervix are of almost equal size, but after the birth of a child the body always remains larger and broader than it was before pregnancy, and the fundus is more markedly curved. During the later years of life, after the cessation of the function of the viscus, the cervix undergoes retrograde changes while the body remains large.
In nulliparae the entire length of the uterus is 5 to 8 cm., about 4 cm. being taken up by the body. The greatest width of the body is 3.5 to 4 cm., and the greatest thickness 2.5 to 3 cm. In multipara the entire length is 6 to 9 cm.; the body is 4.5 cm. long, the cervix 2.5 to 3 cm. long.
The greatest thickness of the body is 3 cm. The uterus of childhood is only 2 to 3 cm. long.
During pregnancy the uterus exhibits an enormous increase in size.
The uterine wall is composed of three layers, the serous coat (perimetrium), the muscular coat {myometrium), and the mucous coat {endometrium). The peritoneum which forms the serous coat is firmly adherent to the muscular coat without the intervention of any subserous tissue, and the musculature is extraordinarily thick, being the largest aggregation of non-striated muscle in the body. It is irregularly arranged and some of the fibers pass into the uterine ligaments of fixation without demarcation.
The uterine mucous membrane is also intimately adherent to the underlying musculature, a submucous layer being absent. In the uterine cavity it is smooth, but in the canal of the cervix it forms a system of folds, the plicae palmatae upon the anterior and posterior walls, which are not obliterated by traction. Each system consists of a median longitudinal ridge with lateral transverse or oblique folds, the longitudinal fold upon the anterior wall being situated slightly toward the right, that of the posterior wall more to the left. The uterine mucous membrane contains the uterine glands; within the cervix they are known as the cervical glands. The surface of the vaginal portion of the cervix is invested by the vaginal mucous membrane.
The parametrium is the connective tissue along the sides of the cervix; it is rich in fat and contains the main arterial ramifications for the uterus. It is continued as a subserous connective tissue upon the posterior and lateral surfaces of the cervix where the peritoneum is not so firmly adherent as is the case upon the uterine body.
Since the uterus is situated centrally in relation with the neighboring portions of the female genitalia, the latter are designated as the uterine adnexa. They consist chiefly of the broad ligaments and their contents (the ovaries and the tubes).
The uterus is held in position by a number of ligaments. The broad ligament (ligamentum latum) is a paired structure derived from the peritoneum, and more or less completely envelops the uterus and tubes. It is attached to the lateral margins of the uterus and consequently forms the mesometrium. The chief fixation of the uterus, however, is due to its intimate connection with the vagina and its consequent attachment to the pelvic floor.
In addition to the broad ligament, the uterus possesses other ligaments which are to be regarded as a continuation of its musculature. The most important of these is the round ligament (ligamentum teres), which is essentially a cylindrical or slightly flattened muscular cord, 12 to 15 cm. in length, which takes origin upon either side from the anterior surface of the uterus in the vicinity of the uterine extremities of the tubes, and runs at first almost horizontally and then forward and downward between the two layers of the broad ligament, covered mainly by the anterior one. It then passes forward and outward along the lateral pelvic wall, enveloped in a fold of peritoneum, like the vas deferens in the male, to the abdominal inguinal ring, and after traversing the inguinal canal, it passes out of the subcutaneous inguinal ring to gradually disappear in the fatty tissue of the labium majus. In the vicinity of the uterus the ligament is thickest and consists solely of connective tissue and non-striated muscle, but in its course through the inguinal canal it usually receives fasciculi of striated muscle fibers from the obliquus abdominis internus and the transversus (analogous to the cremaster in the male), which are continued upon it for a varying distance, frequently extending almost to the uterus, but never passing externally beyond the inguinal canal. The ligament extends about 2 cm. outside of the inguinal canal.
Along with it run the external spermatic vessels of the female.
Similar continuations of the uterine musculature are the mm. rectouterini, which run in peritoneal folds of the same name, and connect the superficial musculature of the rectum with that of the uterus. The uterosacral ligaments are connective-tissue fasciculi which accompany the muscles in the similarly named peritoneal folds to the region of the second and third sacral vertebrae, where they fuse with the periosteum.
The arteries of the uterus are the uterine branches of the internal iliac. They run in the base of the broad ligaments, crossing the ureters 2 cm. from the margin of the uterus and pass inward to the parametrium and the lateral surface of the cervix, along which they run, becoming markedly tortuous (particularly after pregnancy) and rather closely applied to the uterine wall.
The veins form the uterine plexus, a portion of the utero-vaginal plexus. They at first accompany the arteries in pairs, but subsequently form single veins which empty with other venous trunks into the internal iliac vein.
The lymphatic vessels of the cervix empty into the inferior hypogastric glands, while those of the body run to the superior hypogastric and partly also to the lumbar glands.
The nerves are derived partly from the third and fourth sacral nerves and partly from the sympathetic pelvic plexus.

Human Anatomy (1909) by DR. Johannes Sobotta (1869-1945) Professor of Anatomy in the university of Wurzburg.