The testes are located in a skin-covered, highly pigmented, muscular sack called the scrotum that extends from the body behind the penis (see Figure). This location is important in sperm production which occurs within the testes and proceeds more efficiently when the testes are kept 2 to 4°C below core body temperature.
The dartos muscle makes up the subcutaneous muscle layer of the scrotum (Figure). It continues internally to make up the scrotal septum, a wall that divides the scrotum into two compartments each housing one testis. Descending from the internal oblique muscle of the abdominal wall are the two cremaster muscles which cover each testis like a muscular net. By contracting simultaneously, the dartos and cremaster muscles can elevate the testes in cold weather (or water) moving the testes closer to the body and decreasing the surface area of the scrotum to retain heat. Alternatively, as the environmental temperature increases, the scrotum relaxes moving the testes farther from the body core and increasing scrotal surface area which promotes heat loss. Externally, the scrotum has a raised medial thickening on the surface called the raphae.
The testes (singular = testis) are the male gonads—that is, the male reproductive organs. They produce both sperm and androgens such as testosterone and are active throughout the reproductive lifespan of the male.
Paired ovals, the testes are each approximately 4 to 5 cm in length and are housed within the scrotum (see Figure). Sperm develop in structures called seminiferous tubules. During the seventh month of the developmental period of a male fetus, each testis moves through the abdominal musculature to descend into the scrotal cavity. This is called the “descent of the testis.” Cryptorchidism is the clinical term used when one or both of the testes fail to descend into the scrotum prior to birth.
Formed sperm are transferred to the epididymis where they mature. They leave the epididymis during an ejaculation via the ductus deferens. The tightly coiled seminiferous tubules form the bulk of each testis. They are composed of developing sperm cells surrounding a lumen, the hollow center of the tubule where formed sperm are released into the duct system of the testis.