The left cornu and adjacent part of the body of the uterus and the
vagina and vulva are opened up. _1_, Ovary; _2_, Fallopian tube,
with _2′_, its fimbriated end; _3_, cavity of corpus uteri; _4_,
cavity of left cornu; _5_, right cornu, with _5′_, its communication
with the body; _6_, portio vaginalis uteri; _6′_, os uteri; _7_,
broad ligament of uterus; _8_, ligament of ovary; _9_, vagina; _10_,
vulva; _10′_, glandulæ vestibulares majores; _10″_, glandulæ
vestibulares minores; _11_, transverse fold; _12_, external urethral
opening; _13_, _13′_, labia vulvæ; _14_, glans clitoridis; _14′_,
junction of crura to form corpus clitoridis indicated by dotted
lines; _15_, urinary bladder; _a_, utero-ovarian artery with ovarian
(_a′_) and uterine (_a″_) branches; _b_, uterine artery. (After
Ellenberger, in Leisering’s Atlas.)
]
When a soft uterus is distended, the cornua are strongly curved, but
this does not represent the natural form. When fixed _in situ_ the
horns are either slightly curved or nearly straight. The two horns are
commonly unsymmetrical in length and diameter in mares which have
borne young.
The =body= of the uterus (Corpus uteri) is situated partly in the
abdomen, partly in the pelvic cavity. It is cylindrical, but
considerably flattened dorso-ventrally, so that in cross-section it is
elliptical. Its average length is about six inches (15 cm.), and its
diameter, when moderately distended, about four inches (10 cm.). Its
=dorsal surface= (Facies rectalis) is related to the small colon and
rectum. Its =ventral surface= (Facies vesicalis) is in contact with the
bladder, and has inconstant relations with various parts of the
intestine. The term =fundus uteri= is applied to the anterior wide part
from which the cornua diverge.
The position of the body of the uterus is variable, especially in
regard to its anterior part. It is often pressed up against the
rectum, and may be deflected to either side—most frequently to the
left—by the pelvic flexure of the colon or coils of the small colon.
The =cervix= or =neck= of the uterus (Cervix uteri) is the constricted
posterior part which joins the vagina. Part of it (Portio vaginalis
uteri) projects into the cavity of the vagina; it is therefore not
visible externally, but may be felt through the vaginal wall. It is
about two inches (5 cm.) in length, and an inch and a half (3.5 to 4
cm.) in diameter.
=Attachments.=—The body and cornua are attached to the abdominal and
pelvic walls by two extensive peritoneal folds, the =broad ligaments=
(Ligamenta lata). These extend on either side from the sublumbar region
and the lateral pelvic walls to the dorsal border of the cornua and the
lateral margins of the body of the uterus. They contain the vessels and
nerves of the uterus and ovaries, connective tissue, and unstriped
muscular fibers. The ureters are situated along their parietal margins.
The outer layer of each forms a fold, the =round ligament= of the uterus
(Ligamentum teres uteri), which blends with the parietal peritoneum over
the internal inguinal ring; its anterior extremity is situated above the
extremity of the cornu and is rounded and free. It contains muscular
tissue, vessels, and nerves, and is the homologue of the gubernaculum
testis. The anterior part of the neck is continuous with the vagina, and
thus has a more fixed position than the rest of the organ.
=The cavity= of the uterus (Cavum uteri) is largely obliterated in the
non-pregnant state by the contraction of the wall and by folds of the
mucous lining. At the extremity of each cornu it communicates by a
minute opening with the Fallopian tube. The cavity of the neck is termed
the =cervical canal= (Canalis cervicis); it is closed ordinarily by
mucous folds and a plug of mucus. It opens into the vagina by the =os
uteri externum=, and into the body by the =os uteri internum=.
=Structure.=—The wall of the uterus consists of three coats—an external
serous, a middle muscular, and an internal mucous. The =serous coat=
(Perimetrium) is, for the most part, closely adherent to the muscular
coat. It is continuous with the broad ligaments. The =muscular coat=
consists essentially of two layers, a thin external stratum of
longitudinal fibers, and a thick layer of circular fibers. Between these
is a very vascular layer (Stratum vasculare) of connective tissue with
circular and oblique muscular fibers in it. The circular coat is very
thick in the neck, where it forms a =sphincter= half an inch or more
(ca. 1.5 cm.) in thickness. The =mucous membrane= rests directly on the
muscular coat. It is thick, and is covered by columnar epithelium. It
contains numerous long tubular =uterine glands= (Glandulæ uterinæ). It
is brownish-red in color, except in the neck, where it is pale.
=Vessels and Nerves.=—The chief =arteries= are the =uterine= and the
=uterine branch= of the =utero-ovarian=, which have a flexuous course in
the broad ligaments; there is also a branch from the =internal pudic=
artery. The =veins= form pampiniform plexuses and accompany the
arteries. The =lymphatics= are numerous and go to the internal iliac and
lumbar glands. The =nerves= are derived from the sympathetic through the
uterine and pelvic plexuses.
The foregoing statements refer to the non-gravid uterus. In the
pregnant state it undergoes important changes in size, position, and
structure. The increase in size affects chiefly the gravid cornu
(except in the case of twins) and the body. The cornu attains a length
of about two and a half to three feet (ca. 80 to 90 cm.), and a
corresponding diameter; in this process it extends much beyond the
ovary, and the broad ligament. The gravid uterus is entirely abdominal
in position, and extends along the ventral wall, chiefly to the left
of the median plane. It weighs about nine pounds (ca. 4 kg.),
according to Ellenberger. The broad ligaments increase greatly in size
and contain more muscular tissue. The vessels are greatly enlarged and
form new branches. The muscular coat, in spite of the increase in size
and number of the fibers, is somewhat thinner, except in the neck. The
mucous membrane is thicker and more vascular; the epithelium becomes
non-ciliated and stratified.