Vulva
The tract’s external portion that extends from the vagina to the exterior opening is called the vulva. It is the highly vascular and thick fold of skin comprising two lips, namely labia majora and labia minora (singular labium).
The labia majora is analogous to the scrotum of the male. It protects the reproductive tract from the external environment and contains many sebaceous and sweat glands. Two labia are joined at the dorsal and ventral commissure. The dorsal commissure is generally rounded, and the ventral is pointed in all domestic animals, except in horses, where the dorsal commissure is pointed and the ventral commissure is rounded. In small ruminants, the labia are not developed prominently. In ewe, ventral commissure is longer. In sow, the dorsal commissure is wrinkled and has a small number of hairs. In carnivores, the labia are mostly round in shape and generally pigmented with the covering of dense hair. A transverse cutaneous fold appeared at the dorsal commissure, and the ventral one remains as pointed in carnivores. It usually remains as wrinkled and dry. But, under the influence of oestrogen, it became congested with blood and turned swelled and pinkish, a typical oestrus symptom of oestrus. Vulva remains open during mating, oestrus and parturition. It also helps to void the urine.21.7.1 Vestibule
This is a tube-like structure present between the labia and the muscles of the vagina. It extends from the suburethral diverticulum to the external vulva; hence, it performs reproductive and urinary functions. It slops ventrally and opens into the vulva. It is about 10-12 cm long in cow and mare, 5-6 cm in sow, 2.5-3 cm in the ewe, doe and bitch and 0.5-1.5 cm in queen.
21.7.2 Vestibular Glands
There are many glands called vestibular glands or bulbovestibular (Bartholin’s) glands at the vestibule wall.
They are accessory sex glands of the female and resemble the bulbourethral glands of males.
The secretions of these glands act as a lubricant and ease mating and parturition. The vestibular glands can also secret pheromone, which stimulate the males. The vestibular glands are well developed in cows, queens and ewe that open through a single duct on each side of the vestibule. The vestibular glands are smaller in bitch and mare, which open as linear series. Vestibular glands are partially developed in rodents. On the vestibule floor, the remnants of the Wolffian duct are present in the form of a blind pouch called Gartner’s ducts. The prostate gland is partially developed in rodents, bitch, mare and ewe with smaller vestibular glands.21.7.3 VestibularBulbs
It is present on the vestibule wall in mare and bitch. It contains profuse veins (venules) with erectile tissues and is homologous to the cavernous structure of the penis. After intromission, the bulb becomes engorged and erects with the trapping of blood that holds the glans penis, resulting in the locking of the penis.
21.7.4 Hymen
In horses, llamas, elephants, chimpanzees, manatees, whales, guinea pigs and women, a well-developed transverse fold of membranous covering is present at the junction between the vagina and vestibule that partly covers the external vaginal opening, called the hymen. It separates the vagina from the vulva. In domestic animals, it is poorly developed and appears as small oblique folds at the vagino-vestibular junction. It seals the opening of the vagina during the non-breeding season in guinea pigs.
21.7.5 Clitoris
It is a small mass of erectile tissue suspended by a ligament from the pubic bone and found within the ventral commissure of the vulva. It is homologous to the glans penis of the male. Apart from erectile tissue, the clitoris contains tiny blood vessels and sensory nerve endings. The clitoris is very small in small ruminants and sows, and large in carnivores and mares. The body (corpus) and glans (glans clitoridis) have two parts. The body is analogous to the prepuce of a male.
The erectile tissues are elongated and extended internally, called crura. They attach to the ischiatic arch through its left and right branches. Two crura are closely associated with forming the body placed in a fossa, fossa clitoridis, covered with the mucosal fold. The contraction of theTable 21.2 Major characteristics differences of the functional morphology of different female reproductive systems
| Parts of the system | Species | Characteristics |
| Ovary | Cow, sow, ewe, human | Cortex at outside and medulla at inside; ovulation over the entire surface |
| Mare | Cortex and medulla innervated; ovulation occurs only at the ovulation fossa that may result in deep-seated corpus luteum | |
| Fowl | Only left ovary functional; large medullary space with fluid-filled cavities (lacunate); hierarchical follicular growth | |
| Uterus, cervix and vagina | Elephants, rabbits, rodents, opossums, aardvarks | Duplex: two uterine horns, no uterine body, two cervixes, one or two vaginas |
| Cow, ewe, mare, sow, bitch, queen | Bicornuate: two uterine horns, one uterine body, one cervix, one vagina | |
| Primates, monkeys, human | Simplex: no uterine horns, one uterine body, one cervix, one vagina | |
| Fowl | The secondary sex organs are infundibulum, magnum, isthmus, uterus (shell gland), vagina and cloaca | |
| Cervix | Cow, buffalo, ewe | Annular rings—folding of the small smooth musculature |
| Mare | Longitudinal folds | |
| Sow | Interdigitating pads, corkscrew like, no fornix | |
| Bitch, queen | Irregular | |
| Vulva | Cow, ewe, sow, mare | Labia majora |
| Human | Labia majora and minora | |
| Hymen | Ewe, horses, elephants, humans, chimpanzees, manatees, whales, guinea pigs | Well developed |
| Domestic animals | Poorly developed |
vestibular and vulval sphincter muscles elevates the clitoris, and the clitoris protrudes between the vulval lips.
It is called the winking of the clitoris. The clitoris becomes swollen and erect during coitus and has a role in tactile sexual stimulation. The stimulation of clitoris following the artificial insemination has increased the conception rate by promoting LH surge and ovulation.Major characteristics of the functional morphology of female reproductive organs are summarised in Table 21.2.
Know More............
Skene’s glands, also known as periurethral glands, are paired glands situated at the anterior wall of the vagina near the lower urethra, secretes a fluid homologous to plasma ultrafiltrate. These glands are the source of female ejaculate and are considered the ‘female prostate’.
21.8