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Revista chilena de anatomía

Print version ISSN 0716-9868

Rev. chil. anat. vol.19 n.1 Temuco Apr. 2001 


DE Myocastor coypus COIPO)

Antonio E. Felipe*; Alejandra Castro*; Santiago S. Callejas**; Jorge A. Cabodevila**

SUMMARY: The aims of this work was realised the morphological study of the female external genitalia of Myocastor coypus. The vulva was rudimentary and limited by two folds scarcely developed. Its external surface showed a cover with scarce and long hairs while the internal surface had a hairy cover and no pigmentation. The lining of the vulvar area showed a squamous stratified epithelium resting on a lamina propria with many microscopic papillae. In the lamina propria there were abundant small glands of sebaceous aspect associated to pilose follicles of small diameter. The clitoris was a prominent conic structure, with a small glans covered by the prepuce of the clitoris. The prepuce, of rugose surface and soft and flexible consistency, projected point-first towards ventral. The clitoris had a well-developed cavernous body (corpus cavernosum), with muscular tissue in the basal zone, formed the body of the clitoris. The axial part of the body had an elongated hyaline cartilaginous nucleus. The urethral opening was observed as a longitudinal fissure at dorsal of the clitoris, behind the glans.

KEY WORDS: 1. Female external genitalia; 2. Myocastor coypus; 3. Morphology.


The coypu (Myocastor coypus) has been kept in captivity for over 100 years. Although little information has been published on its morphological characteristics of its reproductive system. Some studies on the reproductive aspects of this species have been made in the northern hemisphere (Newson, 1966; Willner et al., 1979; Gosling & Skinner, 1984; Bura, 1992) and in Argentina (Crespo, 1981; Iudica & Alberio, 1995; Felipe et al., 1998). The knowledge about the reproduction of the coypu shows that it is a rodent which keeps in reproductive condition throughout the year and which reaches sexual maturity towards 6 month of age (Baroffio et al., 1979; García Mata, 1985; Iudica & Alberio). The knowledge of the characteristics of the genital organs facilitates the determination of its variations in different stages of the estrous cycle. The aims of this work was to contribute with a characterisation of the anatomy and histology of the female external genitalia of the Myocastor coypus at sexual maturity.


Eleven virgin and sexually mature females of the Silver and Greenland mutations were used. The females were obtained from a breeding farm with corral system and had an average weight of 4.4 ± 0.6 kg and average age of 8,2 ± 1,0 month.

The anatomical description "in situ" included the identification of the organs, the establishment of their relation, the observation of their external conformation, and the determination of their dimensions with a Vernier caliper. The position of the urethral orifice was determined with PC40 sondes attached to syringes containing physiological saline solution and fluorescein as indicating dye, generating from the internal urethral orifice a flow from cranial to caudal. Lately, the complete genital organs were removed to observe the organs in isolation, which allowed deepening in the details and the study of the internal conformation. For the histoarchitectural study the organs were fixed in Bouin's fluid, and kept in 70 per cent alcohol. Routine techniques were used to process the samples until embedding in paraffin wax. Semi-serial 5mm-thick cuts of the areas were made and were stained with haematoxylin/eosin, Mallory´s trichromic, and van Gieson´s trichromic (Prophet et al., 1995). The schemes and the morphological analysis were made with a Wild M3C stereoscopic microscope equipped with drawing camera.

All measurements were expressed as the mean ± sd (Norman & Streiner, 1996).

Fig. 1. General view of the external genitalia of Myocastor coypus.


Macroscopic analysis:The caudal portion of the vagina, at caudal of the ischiatic arc, inclined ventrally until its opening in the vulva. Here, a marked inflexion with the bodily axis, at an angle of almost 45 degrees, was observed. In the animals "in vivo", the vulvar orifice was closed and had the shape of a small fissure with numerous converging low folds. The vulvar orifice had a diameter of 0.9±0.05 cm. This orifice related towards ventral with the clitoris and towards dorsal with the anus, being separated from this last by a distance of 0.22±0.18 cm.

The vulva consisted in a pair of thin folds of limited development. The dorsal commissure appeared rounded, while the ventral one, sharper, was related to the clitoris. This last, partially occluded the vaginal opening at rest. The external vulvar surface, of a greyish colour, showed a cover with long and scarce hairs, while the internal surface was pink and with no hairs.

The clitoris of the coypu was a prominent conic structure, very developed, 0.95±0.05 cm long, lined by a fold of skin, the prepuce of the clitoris, which showed a marked cul-de-sac (preputial cul-de-sac). The prepuce projected point-first towards ventral, exceeding the ventral commissure of the vulva. It had a soft and flexible consistency. Its surface was slightly rugose, with small folds that converged towards a fusiform fissure, located at dorsal of the organ.

The external urethral orifice ended at the same level of the clitoris, behind the rudimentary glans. It had the shape of fusiform longitudinal fissure (see histoarchitectural description of the clitoris).

Histoarchitectural analysis: The lining of the vulvar area showed a squamous stratified epithelium resting on a lamina propria with many microscopic papillas. In the lamina propria corresponding to the folds of the tegument ("vulvar lips") there were abundant small glands of sebaceous aspect associated to pilose follicles of small diameter. The glands had secretory ducts lined by stratified epithelium. The glands as well as the pilose follicles were concentrated towards the external surface of the vulvar lips. There was abundance of adipose tissue. The external layer of the vulvar wall had bunches of muscular fibres of the striated type, surrounded by connective tissue and there was profuse vascularization. There were no lymph nodes but there was an important lymphocytic infiltration.

The clitoris was formed by the glans, the body, and the prepuce. The preputial opening was like a longitudinal fissure at dorsal of the terminal extreme of the prepuce. Its internal surface, forming a starry lumen (prominent mucosal folds) was lined by a squamous stratified epithelium. Its external surface had a squamous epithelium thinner than the internal one but with many micropapillas. The stuffing connective tissue was of the lax type, very vascularized. This, towards the internal zone, had neither glands nor pilose follicles, while in the external surface there were many glands. Those glands were alveolar and of the sebaceous type, with ducts lined by squamous stratified epithelium or cubic biestratified. The glands were associated to pilose follicles as well as independent of them (free sebaceous glands).

The well-developed cavernous body (corpus cavernosum), with muscular tissue in the basal zone, formed the body of the clitoris. The axial part of the body had an elongated hyaline cartilaginous nucleus. The terminal part of the cavernous body (corpus cavernosum) continued on a fibrous body. Surrounding the cavernous body (corpus cavernosum) there was connective tissue arranged as an albugineous tunic (tunica albuginea) with many blood vessels.

At the extreme of the cavernous body there was a glans of limited development, like a connective wrapping of the body. The glans was lined by a flat stratified epithelium resting on connective tissue and lacking lymphonodes.

Fig. 2. Semi-schematic reconstruction of the clitoris of M. coypus (6,4 X) and schemes of transversal sections at different levels (A, B and C, 20 X; D, 12,5 X and E, 8 X).


In general, the anatomy of the external genitalia of the Myocastor coypus was shown similar to described by De Harkness & Wagner (1977), for mice, rats, guinea pigs, hamster and gerbils.

The female external genitalia of coypu, as in other mammal species (Dyce et al., 1987; Priedkalns, 1993), had been represented by the vulva. It was composed by the clitoris, the external urethral orifice and the vulvar´s lips. In the coypu the vulva did not have vaginal vestibule since in this species the external urethral orifice does not ending between the vulvar cavity and the vaginal cavity. This point was considered anatomical conventional limit between the vulva and the vagina (Dyce et al.).

No exist detailed information about the vulva of other hystricomorph rodents, with the exception to the plains viscacha and guinea pig. In the coypu, the vulva was observed to be restricted to a simple orifice surrounded by rudimentary lips as in the plains viscacha (Lagostomus maximus) (Weir, 1971). In all hystricomorph rodents, except the sexually mature coypu, was present a vaginal closure membrane which periodic opening to the recurrence of oestrus behaviour and parturition (Weir, 1974).

The presence of longitudinal folds surrounding the vulva as in the coypu, is a characteristic of the vulva of rodents (Parakkal, 1974; Centola, 1978; Kress et al., 1989) and of adult lagomorphs (Kanagawa et al., 1972).

As in other mammals, the clitoris was an erectile structure. Its body was composed of two small erectile bodies, the corpora cavernosa. The skin over the glans is very thin, forms the prepuce of the clitoris. In all the species the vulvar lips was characterized to present a external hairy cover (Barone, 1996).

The presence of a cartilaginous body in the clitoris coincides with that mentioned by Hillemann et al. (1958) and by Bura et al. (1992) and it was similar to the cat (Barone).

*Área de Ciencias Morfológicas, **Área de Reproducción, Núcleo FISFARVET, Facultad de Ciencias Veterinarias, UNCPBA, Argentina.

RESUMEN: El objetivo de este trabajo fue realizar el estudio morfológico de los órganos genitales externos de Myocastor coypus (coipo). La vulva se presentó rudimentaria y limitada por dos repliegues de escaso desarrollo. Su superficie externa presentó una cubierta de pelos largos y escasos. En la superficie interna de la vulva no hubo pigmentación ni cubierta pilosa. El revestimiento del área vulvar mostró un epitelio escamoso, estraficado, apoyado sobre una lámina propia con papilas microscópicas. En la lamina propia se observaron abundantes y pequeñas glándulas de aspecto sebáceo asociadas a los folículos pilosos. El clítoris fue una estructura cónica prominente, con un glande pequeño y recubierto por el prepucio del clítoris. El prepucio, de superficie rugosa y consistencia blanda y flexible, se proyectó en punta hacia ventral. El clítoris presentó un cuerpo cavernoso bien desarrollado, con tejido muscular en su zona basal, conformando el cuerpo del clítoris. El eje del cuerpo del clítoris presentó un núcleo alargado de cartílago hialino. La abertura uretral se observó a dorsal del clítoris, por detrás del glande.

PALABRAS CLAVE: 1. Órganos genitales femeninos externos ; 2. Myocastor coypus; 3. Morfología.


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Dirección para correspondencia:
Prof. Dr. Antonio Felipe
Facultad de Ciencias Veterinarias
Universidad Nacional del Centro
Pinto 399
Buenos Aires

Recibido : 23-11-2000
Aceptado: 27-12-2000

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