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Anatomy of the Female Reproductive System / 471

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1cm

Caruncles Right uterine Left uterine Uterine Cervix
horn horn body

Figure 26‐7. Cut section of the bovine reproductive tract. The uterine body is relatively short as
compared to the uterine horns in the cow. Source: image courtesy of Library of Reproduction Images
(LORI: http://lorimainsection.blogspot.ca).

the uteri of ruminants; they provide a site Vagina
of attachment for the fetal membranes
(Fig. 26‐7, see Chapter 28). The vagina is the portion of the reproduc-
The cervix of the uterus projects cau- tive tract that lies within the pelvic canal
dally into the vagina. The cervix is a heavy, between the uterus cranially and the vulva
smooth muscle sphincter that is tightly caudally (Figs. 26‐1 and 26‐5). The vagina
closed except during estrus and parturition. is the birth canal for delivery of the fetus at
During estrus the cervix relaxes slightly, parturition and a sheath (vagina is Latin
permitting spermatozoa to enter the uterus. for sheath) for the penis of the male during
In ruminants, and to some extent in sows, copulation (the act of breeding, or service,
the inner surface of the cervix is arranged as it is commonly called in animal
in a series of circular ridges or rings, some- husbandry).
times called annular folds (Fig. 26‐8). The The mucous membrane of the vagina is
cervix of the mare is relatively smooth and glandless stratified squamous epithelium
projects prominently into the vagina, which except in the cow, in which there are some
surrounds the cervix as a deep vaginal mucous cells in the cranial part of the
fornix. vagina adjacent to the cervix. The submu-
The tunica muscularis is the muscular cosa is loose, and the muscular layers con-
portion of the uterine wall, commonly sist of an inner circular and an outer
called the myometrium. It consists of a longitudinal layer of smooth muscle. The
thick inner circular layer of smooth muscle parietal peritoneum invests only on the
and a thinner outer longitudinal layer of cranial part of the vagina, where it lies
smooth muscle, separated by a vascular layer. within the abdominal cavity. The caudal
During pregnancy, the amount of muscle portion of the vagina, passing through the
in the uterine wall increases dramatically, pelvic canal, is covered by pelvic fascia
both in cell size (hypertrophy) and in cell (connective tissue). Ventral to the cranial
numbers (hyperplasia). vagina and uterus is the urinary bladder,