The scrotum is the loose pouch-like sac of skin behind the penis. It contains the testicles, many nerves and blood vessels. The function of the scrotum appears to be to keep the temperature of the testes slightly lower than that of the rest of the body. For human beings, the scrotum temperature should be about 35-36 degrees Celsius (95-96.8 degrees Fahrenheit) , i.e. one to two degrees Celsius below the accepted normal body temperature of 37 degrees Celsius (98.6 degrees Fahrenheit). Higher temperatures may be damaging to sperm count. The temperature is controlled by the scrotum moving the testicles closer to the abdomen when the ambient temperature is cold, and farther away when it is hot. Moving the testes away from the abdomen and increasing the exposed surface area allow a faster dispersion of excess heat. This is done by means of contraction and relaxation of the cremaster muscle in the abdomen and the dartos fascia (muscular tissue under the skin) in the scrotum.