Dartos fascia of scrotum

The Dartos Tunic (tunica dartos) is a thin layer of non-striped muscular fibers, continuous, around the base of the scrotum, with the two layers of the superficial fascia of the groin and the perineum; it sends inward a septum, which divides the scrotal pouch into two cavities for the testes, and extends between the raphé and the under surface of the penis, as far as its root. The dartos tunic is closely united to the skin externally, but connected with the subjacent parts by delicate areolar tissue, upon which it glides with the greatest facility.

In the penis, the loose attachment of the Dartos fascia to Buck's fascia is responsible for the high degree of mobility of the penile skin over the underlying tissus. It is also responsible for carrying the blood supply of the penile skin, a longitudinally-coursing anastamotic network of vessels that arise from the external pudendal vessels.

In the scrotum, 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 thecremasteric reflex.