The extremity of the cornu uteri is opened. _1_, Ovary; _2_, Fallopian
tube, with its ostium abdominale (_2′_), fimbriæ (_2″_), and ostium
uterinum (_2‴_); _3_, cornu uteri, with its mucous lining (_3′_);
_4_, ovarian ligament; _4′_, mesosalpinx. (After Ellenberger, in
Leisering’s Atlas, reduced.)
]
The ovary is attached to the sublumbar region by the anterior part of
the broad ligament; this part of the ligament, the =mesovarium=, is
about three or four inches (ca. 8 to 10 cm.) wide, measured from the
ovary directly to the parietal attachment. The uterine or posterior
extremity of the ovary, is connected with the extremity of the cornu of
the uterus by the =ovarian ligament= (Ligamentum ovarii proprium); this
is a band of unstriped muscle inclosed between the layers of the broad
ligament.
=Structure.=—The greater part of the surface of the ovary has a covering
of peritoneum. The peritoneal investment is absent at the attached
border where the vessels and nerves enter; this area is termed the
=hilus=. The ovulation fossa is covered by a layer of columnar cells, a
remnant of the primitive =germinal epithelium=. The =stroma= of the
ovary (Stroma ovarii) is a network of connective tissue and unstriped
muscular fibers. In the deeper or medullary portion of the stroma (Zona
vasculosa) the meshes are largely occupied by the numerous
blood-vessels. In the peripheral or cortical portion (Zona
parenchymatosa) are numerous =ova= (Ovula) in various stages of
development. The immature ova are surrounded by follicle cells; those
more advanced in development are inclosed also by a condensation of the
stroma termed the =theca folliculi=; within the theca is a quantity of
fluid, the =liquor folliculi=. These constitute the =Graafian follicles=
(Folliculi oöphori), which enlarge as they mature, becoming visible to
the naked eye as vesicles with a diameter of a centimeter or more. When
fully developed, the follicles are superficially situated, and often
project slightly from the surface of the ovary. At intervals follicles
rupture and their contents escape. This process, which sets free the
ovum, is termed =ovulation=; it takes place in the mare only at the
ovulation fossa, and occurs during the periods of œstrum.
[Illustration:
FIG. 409.—SCHEMATIC REPRESENTATION OF CHANGES IN OVARY OF MARE FROM
FŒTAL TO ADULT STATE. (After Born.)
The changes affect chiefly the free border (upper in figure) and the
extent and form of the area covered by germinal epithelium (_4_).
_1_, Peritoneum (broad ligament); _2_, ligament of ovary; _3_,
fimbria of Fallopian tube; _4_, germinal epithelium; _5_, vessels,
which reach the ovary at the attached border (_6_). The latter
represents the hilus, while the deep depression at the free border
is the ovulation fossa. (Ellenberger, in Leisering’s Atlas.)
]
After rupture of a follicle its cavity is partly occupied by a
blood-clot, constituting what may be termed a =corpus rubrum=. By
proliferation and enlargement and fatty changes, the follicle cells
are transformed into lutein cells, forming a yellow mass known as a
=corpus luteum=. If impregnation takes place, the accompanying
increase in vascularity of the organs may cause the corpus luteum to
reach a large size; if impregnation does not occur, it is much
smaller, and is sooner replaced by scar tissue, the =corpus albicans=.
In the young foal the ovaries are large and oval in form. The free
border is convex and is covered by germinal epithelium, which extends
over part of the surfaces also. This area is distinguishable by its
dull gray appearance from the peritoneal surface, which has the usual
smooth glistening character. As growth proceeds the ovary gradually
becomes bent until it assumes its definitive curved shape. The
germinal epithelium is then limited to the ovulation fossa. The ovary
migrates somewhat during development from its primitive position,
which is the same as that of the testicle.
In old animals the ovaries commonly consist largely of fibrous tissue,
in which there are often cysts of various sizes. The ova, present in
enormous number at birth, have then been extruded, or destroyed by
phagocytic action or degeneration.
=Vessels and Nerves.=—The =arteries= of the ovary are derived from the
=ovarian artery=. The artery is relatively large and is flexuous; it
reaches the attached border of the ovary by passing between the layers
of the mesovarium. The veins are large and numerous. They form a plexus
somewhat like that of the spermatic cord. The =lymph vessels= pass to
the lumbar glands. The =nerves= are derived from the sympathetic system
through the renal and aortic plexuses. They accompany the arterial
branches.