Outer-most layer is the scrotal skin, which contains many sweat glands, thermosensitive receptors and sympathetic nerves. The ''tunica dartos'' is a smooth muscle layer found below the skin of the scrotum. In horses, this muscle forms a septum which divides the scrotal sac into right and left compartments. Smooth muscle tone is controlled by androgens released in response to temperature changes, detected by sensory nerves within the scrotal skin. The tunica dartos is responsible for holding the testes close to the body during cold temperatures, as it can maintain sustained contraction, and letting the testes lower in hot weather, increasing the surface area for heat loss from the skin. The next layer is the scrotal fascia. | Outer-most layer is the scrotal skin, which contains many sweat glands, thermosensitive receptors and sympathetic nerves. The ''tunica dartos'' is a smooth muscle layer found below the skin of the scrotum. In horses, this muscle forms a septum which divides the scrotal sac into right and left compartments. Smooth muscle tone is controlled by androgens released in response to temperature changes, detected by sensory nerves within the scrotal skin. The tunica dartos is responsible for holding the testes close to the body during cold temperatures, as it can maintain sustained contraction, and letting the testes lower in hot weather, increasing the surface area for heat loss from the skin. The next layer is the scrotal fascia. |