The =vagina= is the passage which extends horizontally through the
pelvic cavity from the neck of the uterus to the vulva. It is tubular,
is about six to eight inches (ca. 15 to 20 cm.) in length, and, when
slightly distended, about four or five inches (ca. 10 to 12 cm.) in
diameter. Its dilatability appears to be limited only by the pelvic
wall. There is no external line of demarcation between the vagina and
the uterus or the vulva.
It is related dorsally to the rectum, ventrally to the bladder and
urethra, and laterally to the pelvic wall. The recto-genital pouch of
the peritoneum extends between the vagina and rectum for a distance of
about two inches (5 cm.), and ventrally the vesico-genital pouch passes
backward somewhat less between the vagina and bladder. Thus most of the
vagina is retroperitoneal and is surrounded by a quantity of loose
connective tissue, a venous plexus, and a variable amount of fat.
=Structure.=—With the exception of the short peritoneal part, as
indicated above, the proper wall of the vagina is composed of muscular
and mucous coats. The =muscular coat= is composed of a thin layer of
longitudinal fibers, and a thicker layer of circular fibers; it contains
also many elastic fibers. The =mucous coat= is highly elastic, and is
covered with a stratified epithelium. It has no glands.
Under usual conditions the cavity is practically obliterated by
apposition of the walls, so that the lumen is a transverse slit; this
condition is pronounced when the ampulla of the rectum is full. The
anterior end of the vagina is largely occupied by the intravaginal part
of the neck of the uterus, so that the cavity is here reduced to an
annular recess termed the =fornix vaginæ=. The posterior part is
directly continuous with the vulva without any line of demarcation
except the valvular fold, which covers the external urethral orifice; in
very young subjects this fold is continued on either side, forming the
=hymen=, which narrows the entrance to the vagina (Introitus
vaginæ).[152]
=Vessels and Nerves.=—The blood-supply is derived from the branches of
the =internal pudic arteries=. The =veins= form a plexus which is
drained by the =internal pudic veins=. The =lymphatics= pass to the
internal iliac lymph glands. The =nerves= are derived from the
sympathetic through the pelvic plexus.