Anatomical and physiological characteristics of perineal muscles in the female rabbit.

Little information is available on the participation of the perineal striated muscles in female reproductive processes. Here, we describe the gross anatomy and innervation of two striated perineal muscles in the female rabbit, the bulbospongiosus (BSM) and ischiocavernosus (ISM), and analyze their reflex electromyographic (EMG) activity in response to stimulation of the perigenital skin and vaginal tract. Twenty-four mature chinchilla-breed rabbit does were used: 12 to describe the anatomy and innervation of the muscles, 9 to determine reflex EMG activity of the muscles in response to stimulation of the perigenital skin and specific levels of the vaginal tract and 3 to analyze the effect of contraction of the muscles on intravaginal pressure. Both muscles were well developed, with their fibers originating at the ischiadic arch and inserting onto the ligamentum suspensorium clitoridis. Branches of the clitoral and perineal nerves innervated the BSM and ISM, respectively. Bilateral electrical stimulation of these nerves provoked retraction of the clitoral sheath and an increase in intravaginal pressure at the level of the perineal vagina. Whereas neither muscle responded to stimulation of the perigenital skin, both were reflexively activated during mechanical stimulation of the inner walls of the perineal vagina. Prolonged cervical stimulation inhibited this reflex. Thus, in reproductive processes such as copulation and/or parturition, the contraction of these muscles may be induced during stimulation of the perineal vagina.