is a layer of smooth muscular fiber
outside the external spermatic fascia
but below the skin
- In males it is termed tunica dartos and lies beneath the skin of the scrotum. In older males the dartos muscle loses its tone, and tends to cause the scrotum to be smoother and to hang down further.
- In females, the same muscle fibers are less well developed and termed dartos muliebris, lying beneath the skin of the labia majora.
The tunica dartos acts to regulate the temperature
of the testicles
, which promotes spermatogenesis
. It does this by expanding or contracting to wrinkle the scrotal skin.
- Contraction reduces the surface area available for heat loss, thus reducing heat loss and warming the testicles.
- Conversely, expansion increases the surface area, promoting heat loss and thus cooling the testicles.
The dartos muscle works in conjunction with the cremaster muscle to elevate the testis but should not be confused with the cremasteric reflex.
Some dartos-related terms:
- dartoic (dar·to·ic) (dahr-to'ik) of the nature of a dartos; having a slow, involuntary contractility like that of the dartos.
- dartoid (dar·toid) (dahr'toid) resembling the dartos.