Dartos is the only muscle within the wall of the scrotum. It is a sheet of smooth muscle. It arises from the layer superficial to the superfical fascia. It passes superficially to insert into the skin and midline fibrous raphe of the scrotum.
It is innervated by sympathetic fibres from the genital branch of the genitofemoral nerve (L1, L2).
Dartos acts to regulate the temperature of the scrotum. It does this by contracting to wrinkle the scrotal skin. This reduces the surface area available for heat loss. Temperature regulation is important for optimal spermatogenesis.