The =vulva= or =urogenital sinus= is the terminal part of the genital
tract.[153] It is continuous in front with the vagina, and opens
externally at the vulvar cleft below the anus. There is no external line
of demarcation between the vagina and vulva. The tube is about five
inches (ca. 12 cm.) in length, measured from the external urethral
orifice to the inferior commissure; dorsally it is considerably shorter.
It is related dorsally to the rectum and anus, ventrally to the pelvic
floor, and laterally to the sacro-sciatic ligament, the semimembranosus
muscle, and the internal pudic artery. The external orifice or =vulvar
cleft= (Rima vulvæ) has the form of a vertical slit, about four to six
inches (ca. 10 to 15 cm.) high, and is margined by two prominent rounded
folds, the labia. The =labia= of the vulva (Labia vulvæ) meet above at
an acute angle, forming the =superior commissure= (Commissura dorsalis),
which is about two inches (ca. 5 cm.) below the anus. Below they unite
to form the thick rounded =inferior commissure= (Commissura ventralis),
which lies about two inches (ca. 5 cm.) behind and below the ischial
arch. When the labia are drawn apart, a rounded body, about an inch (ca.
2.5 cm.) wide, is seen in the inferior commissure; this is the =glans
clitoridis=, the homologue of the glans penis. Overlying it is a thin
fold, the =prepuce= of the clitoris (Præputium clitoridis). At the
anterior extremity of the ventral wall of the vulva, _i. e._, about four
or five inches (ca. 10 to 12 cm.) from the inferior commissure, is the
=external urethral orifice= or meatus urinarius (Orificium urethræ
externum). It readily admits the finger and is very dilatable. It is
covered by a fold of mucous membrane, the free edge of which is directed
backward.
=Structure.=—The =labia= are covered by thin, pigmented, smooth skin,
which is richly supplied with sebaceous and sweat glands. This is
continuous at a distance of about half an inch (ca. 1 to 1.5 cm.) from
the free edge with a thin glandless mucous membrane. Between these is a
layer of striped muscle, the =constrictor vulvæ=; this fuses above with
the sphincter ani, and embraces the clitoris below, spreading out
laterally at the inferior commissure. It constricts the vulvar orifice
and elevates the clitoris. The =constrictor vestibuli= muscle embraces
the vulva in front of the preceding; it is joined on either side by a
band of unstriped muscle which arises from the first and second
coccygeal vertebræ, and is homologous with the proximal part of the
retractor penis. It constricts the vulva. Under this muscle in the
lateral wall is a flattened, oval body, the =bulbus vestibuli= (Fig.
453); this is an erectile structure, homologous with the corpus
spongiosum urethræ of the male. It is about two and a half to three
inches (ca. 6 to 8 cm.) long, and an inch or more (ca. 3 cm.) wide. It
consists of a venous network inclosed in a fibrous capsule, and is
supplied with blood by a large branch of the internal pudic artery. The
=mucous membrane= of the vulva is reddish in color, and forms
longitudinal and transverse folds. It presents ventrally two linear
series of small papillæ which converge toward the inferior commissure;
these mark the orifices of the ducts of the =glandulæ vestibulares
minores=. On either side of the dorsal wall is a group of eight to ten
larger prominences on which the ducts of the =glandulæ vestibulares
majores= (of Bartholin) open.
Quite exceptionally there may be found on either side of the urethral
orifice the opening of the canals of Gartner (Ductus epoöphori
longitudinales).
The =clitoris= is the homologue of the penis. It arises from the ischial
arch by two crura, which unite to form a =body= as large as one’s little
finger. This projects backward into the inferior commissure of the
vulva, capped by a small rounded =glans=. The organ is composed of
erectile tissue similar to the corpus cavernosum penis. The
=ischio-cavernosus= (or erector clitoridis) is a very feeble muscle
which depresses the clitoris. The veins of the clitoris communicate by
an intermediate plexus on either side with the bulbus vestibuli.