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Schaffer, N.E.; Beehler, B.A., 1990. Preliminary studies on the anatomy and ultrasonic images of the reproductive structure of three species of rhinoceros (Rhinoceros unicornis, Diceros bicornis, Ceratotherium simum). Proceedings of the American Association of Zoo Veterinarians 1990: 242-248, 2 figures, 1 table

Location: World
Subject: Anatomy - Reproductive organs
Species: Black Rhino

Original text on this topic:
The vagina is smooth with large longitudinal folds that course between the urethral opening and the cervix. In a nulliparous D. bicornis, a hymen blocked the vaginal canal just cranial to the urethral opening. This mucous membrane blockage was perforated by a hole. A septum through the hole divided it further into 2 separate 3.0-4.0 mm holes. The cervix of the non-pregnant uterus was most often associated with the internal brim of the pelvis. Interdigitating folds of the cervix resulted in a convoluted lumen. Both the internal and external os are undefined due to the many folds that surround the openings.
On ultrasonic, longitudinal cross-sectioning, the cervix appears as interlocking swirls. The cervix appeared tightly closed in all female rhinos examined with the exception of R. unicornis, SB#361. On ultrasound examination this rhinoceros exhibited follicular development and an open passage could be followed through the folds of the cervix.
Approximately 3.0 cm cranial to the internal os of the cervix, the horns of the bicornate uterus are joined at the muscular layer. They remain united for as much as 20.0-30.0 cm before separating to continue on to the ovaries. This creates a septum in the body of the uterus. The lumen of the uterine horn in the nonpregnant animal often had a starburst appearance on cross-sectional ultrasound. This is due to the many long, thin folds in the endometrial mucosa. In the African rhinos examined, they were approximately 2.0-4.0 mm wide and extended into the lumen from 3.0-8.0 mm. However, the endometrium will vary widely depending on the stage of the estrus cycle. The uterus courses cranially at a ventrally convex curve from the cervix toward the kidneys to the ovaries. The ovaries lie less than 1.0 cm from the end of the uterine horn, in the broad ligament that hangs from the dorsal abdominal cavity. The ovary occupies one edge of a deep ovarian bursa, the oviduct courses through the bursa to the long fimbriated infundibulum which lies along the opposite bursal border and appears to cover the entire ovary. In D. bicornis and Ceratotherium simum, the inactive ovaries are flat and oval. In one D.bicornis, the ovaries were spheroids (3.8 cm x 4.5cm) with several follicles on both ovaries, 1.0-3.0 cm in diameter, and 1 corpus luteum of 0.8 cm x 1.2 cm on 1 ovary. In a C. simum, there was a well organized corpus luteum (2.8 cm x 1.0 cm) protruding from the surface of the right ovary; and a corpus hemorrhagica (2.2 cm x 2.6 cm) on the surface of the left ovary. With ultrasound imaging in a R. unicorns, there were spherical ovaries 8.0 cm in diameter, and the left ovary had a follicle of 3.2 cm in diameter protruding slightly from the surface.

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