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Lab 6A, 8A, 9A: Inguinal Canal and Comparative Female Genitalia 1

Learning Objectives

  • Review inguinal canal anatomy in the female domestic species.
  • Define the pelvic cavity pouches surrounding the pelvic viscera and specifically understand the anatomical importance of foaling injuries in the mare in relation to the peritoneal reflections in the pelvic cavity.
  • Identify the major features of the female reproductive tract in the domestic species.
  • Relate the genital anatomy of the female domestic species to clinical conditions.

Female Reproductive Tracts

Observe: Use wet prosections of female reproductive tracts and female cadavers to identify the structures in this section.

Carnivores

Ovaries and associated structures

The ovaries are located near the caudal pole of the kidneys. The right ovary lies cranial to the left ovary and is dorsal to the descending duodenum. The left ovary is between the descending colon and the abdominal wall. Each ovary is enclosed in a thin-walled peritoneal sac, the ovarian bursa, formed by the mesovarium and mesosalpinx. The ovarian bursa is open to the peritoneal cavity by means of a slit-like orifice on the medial surface.

The uterine tube courses cranially and then caudally through the lateral wall of the bursa on its way to the uterine horn.

The infundibulum is the dilated ovarian end of the uterine tube. It has a fimbriated margin and functions to engulf the oocyte after ovulation.  Note that several of the fimbriae protrude into the peritoneal cavity from the opening of the ovarian bursa.  In life, these fimbriae function to close the opening into the peritoneal cavity at the time of ovulation and thus prevent transperitoneal migration of oocytes. The entrance of the infundibulum into the uterine tube is often described as the abdominal ostium, and it is in this region that fertilization takes place. The uterine tube is short and slender. It opens into the much wider uterine horn at the tubouterine junction. This region is of physiological importance because it is here that sperm and ova are regulated in their transit.

Observe: Examine the lateral surface of the ovarian bursa and observe the small cord-like thickening within its wall. This is the uterine tube.   In female cadavers, open the ovarian bursa and examine the ovary and the infundibulum.

Connecting Peritoneal Structures of the Female Reproductive tract

The broad ligaments of the uterus are the connecting peritoneum folds on each side that attach to the lateral sublumbar region. They suspend all the internal genitalia except the caudal part of the vagina, which is not covered by peritoneum.

Each ligament is divided into three parts: The mesometrium arises from the lateral wall of the pelvis and the lateral part of the sublumbar region and attaches to the lateral part of the cranial end of the vagina, uterine cervix, and uterine body, and the corresponding uterine horn. The mesovarium, a continuation of the mesometrium, is the cranial part of the broad ligament. It begins at a transverse plane through the cranial end of the uterine horn and attaches the ovary and the ligaments associated with the ovary to the lateral part of the sublumbar region. The mesosalpinx is the peritoneum that attaches the uterine tube to the mesovarium and forms with the mesovarium the wall of the ovarian bursa.

The suspensory ligament of the ovary joins the transversalis fascia medial to the dorsal end of the last rib. It is the thickened, fibrous, cranial margin of the broad ligament (specifically, the mesovarium). It functions to hold the ovary in a relatively fixed position.  During an ovariohysterectomy (spay) this ligament is disrupted (torn, stretched, or sharply cut) at approximately its midpoint, to release the tight restraint on the ovary and thereby facilitate exteriorization of the ovary for its removal.

The proper ligament of the ovary is short and attaches the ovary to the cranial end of the uterine horn. From this point caudolaterally to the deep inguinal ring and inguinal canal, there is a peritoneal fold from the lateral layer of the mesometrium (subpart of the broad ligament connection the uterus to the body wall) that contains the round ligament of the uterus in its free border. The round ligament of the uterus, a homologue of the embryonic gubernaculum, has no function in the adult. It passes through the inguinal canal and is wrapped by the vaginal process and adipose tissue in the canine. In the queen, the vaginal process is absent and the round ligament does not extend further than the deep inguinal ring.

Observe: Identify the connecting peritoneal structures of the female reproductive tract bolded above.

Intrapelvic female reproductive tract

The cervix is the constricted caudal portion of the uterus. It forms a small palpable enlargement just caudal to the short body of the uterus. The cervical canal is in a nearly vertical position, with the uterine opening (internal uterine ostium) dorsal and the vaginal opening (external uterine ostium) ventral in position.

The vagina is located between the uterine cervix and the vestibule. The most cranial part of the vagina is the fornix, which extends cranial to the cervix along its ventral margin. The mucosal lining of the remaining part of the vagina is thrown into longitudinal folds that have small transverse folds. These are evidence of its ability to enlarge in both diameter and length. The longitudinal folds end dorsally at the level of the external urethral orifice, where the vagina joins the vestibule. A prominent dorsal longitudinal fold in the cranial vagina nearly obscures the external urethral ostium and makes urinary bladder catheterization difficult.

The vestibule is the cavity that extends from the vagina to the vulva. The urethral tubercle projects from the floor of the cranial part of the vestibule. The urethra opens on this tubercle. This tubercle is at the level of the ischial arch. Note its relationship to the more ventrally placed vulva.

In the floor and ventrolateral wall of the vestibule, deep to the mucosa, are two elongated masses of erectile tissue, the vestibular bulbs. They are homologous to the bulbs of the penis of the male and lie in close proximity to the body of the clitoris. They are difficult to distinguish unless your incision passed through them.  See if you can find the vestibular bulbs in the prosections, but do not worry if you cannot locate them. Make sure to know these structures conceptually.

The clitoris is the female homologue of the penis. It is a small structure located in the floor of the vestibule near the vulva. It is composed of paired crura, a short body, and a glans clitoridis, which are difficult to distinguish. The glans clitoridis is a very small erectile structure that lies in the fossa clitoridis. The fossa is a diverticulum or recess as much as 2-3 cm deep in the floor of the bitch’s vestibule and should not be mistaken as the urethral opening. This anatomy is important when passing a urethral catheter in the female patient.  The dorsal wall of the fossa partly covers the glans clitoridis and is homologous to the male prepuce. Note that in the queen, the vulva of the cat is small and inconspicuous in the non-estrus, non-pregnant state.  The clitoris of the queen is poorly developed. The fossa clitoridis is represented by a small depression just inside the vulva. The fossa clitoridis should not be mistaken for the external urethral orifice.

FYI:  The retractor clitoridis muscle, a homologue of the retractor penis in the male, originates on the first two caudal vertebrae, joins the external anal sphincter, blends with the constrictor vulvae, and continues onto the ventral surface of the clitoris.

Observe the course of the female urethra.  It extends from the bladder caudodorsally over the cranial edge of the pelvic symphysis to the genital tract caudal to the vaginovestibular junction. It ends at the external urethral orifice on the urethral tubercle, which is dorsal to the rima pudendi at the level of the ischial arch.

Observe: Use wet prosections of female carnivore reproductive tracts to identify the structures bolded above.

 

Clinical Application: Urinary Catheterization in the Female Carnivore

While passing a urinary catheter in a male carnivore is a much more commonly performed procedure, usually due to urethral obstruction, it is at times necessary to pass a urinary catheter in a female animal.  Doing so is more challenging due to the location of the external urethral orifice at the boundary between the vestibule and vagina.  To facilitate placement, place a finger over the catheter and keep it on the ventral wall of the vestibule as it is advanced cranially. Doing so will help to ensure the catheter enters the pelvic urethra rather than the vagina, which is located dorsal to the urethra.  Advance the catheter until urine begins to flow through it.

 

External Genitalia

The vulva includes the two labia and the external urogenital orifice that they bound, the rima pudendi. The labia fuse above and below the rima pudendi to form dorsal and ventral commissures. The dorsal commissure is ventral to a dorsal plane through the pelvic symphysis. The ventral commissure is directed caudoventrally.

Observe: Identify the vulva and its dorsal and ventral commissures.

Clinical Relavance:  Hooded/Recessed Vulva

A hooded vulva describes a condition where excess perineal skin folds and/or fat cover the vulva, predisposing the patient to urinary tract infections and urine scalding. To correct this condition, a surgical procedure called a vulvoplasty or episioplasty may be performed.

Peritoneal Pouches

From dorsal to ventral, the viscera of the pelvic cavity are the rectum, reproductive tract [vagina (females) or genital fold (males)], and the urinary bladder.

The parietal peritoneum of the abdominal cavity extends part way into the pelvic cavity and reflects back on itself, forming blind-ended pouches around and between the viscera of the pelvic cavity. This line of peritoneal reflection marks the caudal extent of the peritoneal cavity.  Examine the pelvic cavity of the cadaver and identify the organs present (transected rectum, reproductive organs, urinary bladder). Then identify the peritoneal pouches by boldly passing your hand caudally around the pelvic cavity viscera and between the connecting peritoneums.  The rectogenital pouch is between the rectum and genital tract (uterus in female, genital fold containing ductus deferens in male); on either side of the rectum and mesorectum (connecting peritoneum of the rectum) continuing dorsally from the rectogenital pouch is the pararectal fossa; between the genital tract and the urinary bladder is the vesicogenital pouch; and between the pubis and the urinary bladder (ventral to the lateral ligaments of the bladder) is the pubovesical pouch.

 

Observe:  Examine the pelvic cavity of all cadavers and identify the organs present (transected rectum, reproductive organs, urinary bladder). Then identify the peritoneal pouches by boldly passing your hand caudally around the pelvic cavity viscera and between the connecting peritonea.

 

Clinical Application:  Rectovaginal Fistulas/Rectal Tears

Pay particular attention to the caudal extent of the rectogenital pouch (it is caudal to the cervix). The prognosis for tears to the rectum (iatrogenic during palpation per rectum, or from breeding and parturition accidents) and tears to the vagina (breeding or more commonly parturition injuries) is in large part dependent on whether the tear is cranial to the caudal extent of the pouch and thus communicating with the peritoneal cavity.  This is especially important in the mare where foaling injuries from a misdirected foot can cause tears through the dorsal vaginal wall and on into the rectum. If the perforation occurs cranial to the line of peritoneal reflection and involves the rectum, then the peritoneal cavity will become contaminated with fecal materal, an emergency condition that may be fatal for the horse due to the severe sepsis that likely ensues. A tear caudal to the peritoneal reflection will be considered retroperitoneal and therefore much less life-threatening but it still typically requires significant attention. If the foot is subsequently retracted back into the vagina before parturition progresses a rectovaginal fistula will result; if the foot stays in the rectum, a 3rd degree perineal laceration occurs as the foal is born, tearing the vaginal roof, the intervening perineal tissues (the perineal body), and the rectal floor all the way out through the anal sphincter and skin surface. Perineal lacerations are graded on their severity and 1st and 2nd degree lacerations do not enter the rectum and are more readily managed.

Examining a foaling injury about 3 months post foaling in a mare.

Q: What is your diagnosis?

Answer

Ungulate Female Genital Tracts

Observe: Identify the bolded structures on cadavers where visible, and otherwise make liberal use of the wet reproductive tract specimens to understand this anatomy on all of the female ungulate species.

Broad ligament review

The broad ligaments are the two connecting peritoneums that attach the female reproductive tract to the body wall. Each ligament is divided into several parts, named according to the specific part of the internal genitalia supported by the ligament: the mesovarium directly supports the ovary and its cranial, thickened border is the suspensory ligament of the ovary; the mesosalpinx (a fold detached from the mesovarium) which contains the uterine tube and forms the lateral wall of the ovarian bursa; the mesometrium, which supports the uterus. The round ligament of the uterus generally passes from the tip of the uterine horn to the deep inguinal ring in a lateral fold of the broad ligament (mesometrium part).

Observe: Examine dissected cadavers to identify this anatomy: broad ligament- mesovarium, mesosalpinx, mesometrium, round ligament of the uterus (mare, maybe doe,), suspensory ligament of the ovary.

Ovaries and Associated structures

Note that the ovaries of the mare are relatively large structures and, in the adult, are characterized by their unusual kidney shape. This unique shape is produced by the presence of a distinct depression, the ovulation fossa, which develops as the ovary matures.  As the name implies, rupture of the follicle (ovulation) typically occurs at or near the ovulation
fossa.

The ovaries are tightly connected to the uterine horns via a band of fibrous tissue and smooth muscle, the proper ligament of the ovary. In the cow, both the mature follicle and corpus luteum project prominently from the surface of
the ovary, and can be palpated rectally.

The ovarian bursa is a cavity that surrounds the ovary, enclosed by the mesovarium, mesosalpinx and ovary. Unlike that of the dog, the ovarian bursa of domestic ungulates is rather open. That is, the mesosalpinx, which contains the uterine tube, only loosely envelops the ovary and can be easily reflected to expose the ovary. The uterine tube, with its funnel-shaped beginning (the infundibulum with finger-like fimbriae around its margin) passes from adjacent to the ovary to its opening into the tip of the uterine horn. In the center of the infundibulum is the abdominal opening of the uterine tube, through which ova pass.

Observe: Identify the following structures as described above, in all of the ungulate species:  ovary, ovarian bursa, ovulation fossa (mare), uterine tube, infundibulum (with fimbriae), abdominal opening of the uterine tube, ovarian a., ovarian v., proper ligament of ovary.

Uterus

The proximal halves of the uterine horns lie close together and are connected by the intercornual ligament(s) in ruminants. In the cow, distinct dorsal and ventral intercornual ligaments are present. During rectal palpation, the dorsal intercornual ligament can be used as a finger hold to bring the non-gravid uterus into the hand for examination. In the doe and ewe a singular intercornual ligament is present.

The uterine body is of variable length between the species.

Cow:  The cervix of the cow is firm and thick-walled, which allows it to be easily identified during rectal palpation of the genital tract. Note that it has three or four prominent circular folds that project into the lumen of the cervical canal. When the cervix is closed, these folds interdigitate with one another and make passage of an insemination pipette virtually impossible. During pregnancy, the canal is completely sealed with a tight-fitting mucous plug.

Goat:  The cervical canal of the small ruminants has more circular folds than that of the cow.

 

Sow:   The cervix of the sow is especially long, and the canal is closed by the interdigitation of a series of prominences (cushions), from the cervical wall into the lumen.

Mare:  In the mare, the appearance of the cervix varies considerably and, when viewed through a vaginal speculum, is used to evaluate the stage of the reproductive cycle. The cervix opens into the uterine body at the internal uterine (or cervical) ostium and to the vagina at the external uterine (or cervical) ostium.

Observe: In the cow, identify the intercornual ligament, and identify the uterine body (short in ruminants, long in mare), cervix, and internal and external uterine openings (ostium) in all of the ungulates.  Identify the cervical cushions (sow).

Vagina

The vagina has circular and longitudinal mucosal folds, allowing for distension during parturition. Note the projection of the cervix into the vagina (referred to as the cervix portio vaginalis). Identify the recess around the projecting cervix – it is known as the vaginal fornix.  The vaginal fornix must be avoided when attempting to insert an insemination pipette into the external ostium of the uterus. In the small ruminants, the intravaginal part of the cervix lies in a ventral depression so that the external uterine ostium is more on a level with the ventral floor of the vagina. The sow has no intravaginal portion of the cervix, and therefore no fornix vaginae, the sow vagina is relatively long and is characterized by prominent longitudinal folds

Observe: Identify the vagina in all species and the vaginal fornix (mare, cow, doe).

Vestibule and urethra

The vestibule extends from the vagina to the vulva. Locate the cranial extent which is identified by the external urethral orifice of the urethra, covered partially by a transverse fold which is continued either side as a remnant of the hymen in the mare. The vestibule of the pig is long (have you picked up by now that basically the sow reproductive tract is looooonnngg? Except for the short uterine body!), so the external urethral orifice is located relatively far cranially. In the ruminant and sow, a blind recess is present ventral to the external opening of the urethra, the suburethral diverticulum. Like almost everything else in the female urogenital tract of the pig, the urethra is long, so that only the neck of the urinary bladder is located within the pelvic cavity. The urethra of the mare is especially short and wide (enough so that a relatively small, well lubricated hand can be gently passed through and into the bladder to retrieve a cystic calculus! Such calculi are uncommonly identified in mares, one reason being that any developing stones are readily passed out in the urine).

FYI – In the mare, there is erectile tissue in the lateral walls of the vestibule that is consolidated to form the right and left vestibular bulbs. Although erectile tissue is present in the other domestic ungulates, it is more diffuse. In the dorsal, lateral and ventral walls of the vestibule, depending on the species, small openings indicate the presence of vestibular glands (major and minor vestibular glands are described). Major vestibular glands represent the female homologues of the bulbourethral glands of the male.

Observe: Identify the vestibule, urethra, external urethral orifice in all the ungulates and the suburethral diverticulum in the ruminant and sow.

Clinical relevance:  suburethral diverticulum in passing a urinary catheter or artificial insemination pipette

The suburethral diverticulum must be taken into account during catheterization of the urinary bladder of the ruminant or sow. How would you avoid it?

Vulva and clitoris

The labia of the equine vulva are rounded, and the vulvar cleft is unique in that the ventral commissure is rounded and the dorsal commissure pointed, just the opposite of the other domestic mammals.

In the cow, the small glans clitoridis is located just inside the ventral commissure. The glans clitoridis of the sow, is also rather poorly developed and is concealed in its small fossa, just inside the ventral commissure of the vulva.

The clitoris of the mare is large and contains a considerable quantity of erectile tissue. Like its male homologue (glans penis), the glans clitoridis of the horse is better developed than that of other species. The glans clitoridis is located within the fossa clitoridis. The glans clitoridis has a median sinus clitoridis (maybe referred to as the fossa glandis) and two inconstant lateral clitoral sinuses present within its structure (in the gelding/stallion, the fossa glandis is located in the glans penis and surrounds the urethral process at the end of the urethra).

Observe: Identify the vulva, vulvar cleft, labia, clitoris, glans clitoridis, fossa clitoridis (mare) and sinus clitoridis (mare).

Clinical relevance:  Contagious equine metritis and “Winking”

The clitoral sinuses have been shown to harbor the infectious organism responsible for contagious equine metritis (Taylorella equigenitalis).

During estrus or following urination, mares can voluntarily contract their ischiocavernosus muscles and expose the glans clitoridis, a phenomenon that, for lack of a more appropriate term, is known as “winking.”

Clinical Relevance:  Caslick’s vulvoplasty

In the mare, the relationship of the vulva and vestibule to the ischial arch and anus is important. Poor perineal conformation, loss of body condition, and increasing age can result in the vulva and anus drawing cranially or ‘sinking’, as if they were falling into the pelvic cavity. This predisposes to fecal contamination of the vulva and a loss of normal vulva sealing such that air and contaminates can enter the vestibule and vagina. To compound matters, the vulva tends to fall in and out of the pelvic outlet as the mare walks. This to-and-fro motion tends to pump air into the vestibule and vagina (‘windsucking’), causing a pneumovagina.

To manage this condition, many brood mares undergo a procedure known as a Caslick’s vulvoplasty (simply, a ‘Caslick’s’). The vulvar cleft is sutured closed, except for an opening at the ventral commissure, to allow for urination. The vulva is reopened before parturition to avoid excessive foaling trauma!

 

Clinical Relevance:  Urovagina

In older mares, poor perineal conformation and poor body condition can also result in urine pooling in the vagina (urovagina), resulting in vaginitis and possibly metritis. ‘Urethral extension’ surgery can help and involves using the transverse fold at the external urethral orifice as a flap of tissue that can be sutured caudally to additional flaps of tissue to create a tunnel leading from the urethral orifice. This tunnel directs the urine more caudally and limits retrograde flow and pooling of urine back into the vagina.

 

Review videos

Female dog reproductive tract, cadaver and wet specimen – 16 min

Female dog repro, wet specimen – 5 min

Dr. Gallenstein explains the anatomy of a dog spay  – 8 min

Mare Pelvic Cavity  – 15 minutes

 Mare repro tract  – 7 minutes

 Cow repro tract – 8 minutes

 Sow repro tract  – 7 minutes

Udder, placenta – 6 minutes

Placentation review – 10 minutes

Terms

Ovaries, Uterus, and Associated Structures
Term Features Species differences/comments
Ovaries
Ovarian bursa
Ovulation fossa ID in mare only
Mesovarium
Mesosalpinx
Infundibulum
Uterus
Uterine horns
Intercornual ligaments ID in bovine only
Uterine tube
Abdominal opening of the uterine tube
Uterine body
Cervix
Internal uterine ostium
External uterine ostium

 

Intrapelvic Female Reproductive Tract
Term Features Species differences/comments
Vagina
Vaginal Fornix Not in the sow
Vestibule
Vestibular bulbs Do not ID.  Know what and where they are
Urethra
Suburethral diverticulum Ruminant and Sow only
External urethral orifice
Urethral tubercle
Vulva
Labia
Vulvar cleft
Ventral commissure
Dorsal commissure
Clitoris/Glans clitoridis
Fossa clitoridis
Sinus clitoridis ID in mare only

 

Connecting Peritoneal Structures of the Female Reproductive Tract
Term Features Species differences/comments
Broad ligaments
Mesometrium
Mesovarium
Mesosalpinx
Suspensory ligament
Proper ligament of the ovary
Round ligament of the uterus
Vaginal Process dog only

 

Peritoneal Pouches
Term Features Species differences/comments
Rectum
Line of peritoneal reflection ID in mare only
Urinary bladder
Rectogenital pouch ID in mare only
Genital fold
Mesorectum
Pararectal fossa ID in mare only
Vesicogenital pouch ID in mare only
Pubovesical pouch ID in mare only

 

A. Identify the structure
B. The tip of the pin is in what space?
A. Identify the pinned connecting peritoneum
B. A is the connecting peritoneum for what structure?
A. Identify the pinned feature
B. The pin is entering what space?
.

 

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