Although dermal smooth muscles (DSM) are mentioned in the female genital region, , no systematic analysis and description of these muscles is published to date to the best of our knowledge.
The appearance of the DSM was studied in 7 human female cadavers (age range between 64–98 years and no pathologic conditions affecting this region) using 10 μm thick serial sections (at least 10 equally distributed cross-sectional areas from the pubic region toward the perineal body) of paraffin-embedded tissue samples (hematoxylin and eosin staining) and antibodies against smooth muscle alpha actin (dilution 1:150; Sigma-Aldrich, St. Louis, Missouri) and against neurofilaments (dilution 1:1000, clone 2F11; Dako, Glostrup, Denmark) to observe the general innervation pattern, against tyrosine hydroxylase (dilution 1:200; Biological Divisions, Rogers, P40101-0) to investigate sympathetic innervation, and against connexin 43 (dilution 1:200; Sigma-Aldrich) to proof intercell-connection.
In all the female specimens, DSM were present in and restricted to the labia majora ( Figure ) . The DSM bundles were located within the vein-rich dermis (distance of the DSM bundles toward the epidermis between 200–600 μm) and formed a 0.6 mm to –2.5 mm thick layer, always interwoven with loosely connective tissue without fat cells. The ventral border showed only single smooth muscle bundles extending into the pubic region. They remained strictly on each side and showed no communication. There were no DSM within the labia minora or toward the clitoris. A thick layer of fatty connective tissue separated the DSM from the striated genital muscles and the vestibular bulbs. Toward the dorsal border, the DSM oriented medially but showed no clear communication with the deeper smooth muscle bundles in the subcutis of the perineal body. These deeper smooth muscles (distance of 3.6–4.0 mm toward the epidermis) were connected to the striated muscles of the perineal body. Virtually all DSM bundles showed a ventral-dorsal orientation.