In most terrestrial mammals, the scrotum (pl.: scrotums or scrota; possibly from Latin scortum, meaning "hide" or "skin")^[1][2] or scrotal sac is a part of the external male genitalia located at the base of the penis. It consists of a sac of skin containing the external spermatic fascia, testicles, epididymides, and vasa deferentia. The scrotum will usually tighten during penile erection and when exposed to cold temperatures.

The scrotum is homologous to the labia majora in females.

In regards to humans, the scrotum is a suspended dual-chambered sac of skin and muscular tissue containing the testicles and the lower part of the spermatic cords. It is located behind the penis and above the perineum. The perineal raphe is a small, vertical ridge of skin that expands from the anus and runs through the middle of the scrotum front to back. The scrotum is also a distention of the perineum and carries some abdominal tissues into its cavity including the testicular artery, testicular vein, and pampiniform plexus.

Internal structure

Additional tissues and organs reside inside the scrotum and are described in more detail in the following articles:

• Appendix of epididymidis
• Cremaster muscle
• Dartos fascia
• Efferent ductules
• Epididymis
• Leydig cell
• Lobules of testis
• Paradidymis
• Rete testes
• Scrotal septum
• Seminiferous tubule
• Sertoli cell
• Spermatic cord
• Testicle
• Tunica albuginea of testis
• Tunica vaginalis
• Tunica vasculosa testis
• Vas deferens

During the fifth week after fertilization, the genital ridge grows behind the peritoneal membrane. By the sixth week, string-like tissues called primary sex cords form within the enlarging genital ridge. Externally, a swelling called the genital tubercule appears over the cloacal membrane.

Testosterone secretion starts during week eight, reaches peak levels during week 13 and eventually declines to very low levels by the end of the second trimester. The testosterone causes the masculinization of the labioscrotal folds into the scrotum. The scrotal raphe is formed when the embryonic, urethral groove closes by week 12.^[10]

The scrotum regulates the temperature of the testicles and maintains it at 35 degrees Celsius (95 degrees Fahrenheit), i.e. two or three degrees below the body temperature of 37 degrees Celsius (99 degrees Fahrenheit). Higher temperatures affect spermatogenesis.^[12] Temperature control is accomplished by the smooth muscles of the scrotum moving the testicles either closer to or further away from the abdomen dependent upon the ambient temperature. This is accomplished by the cremaster muscle in the abdomen and the dartos fascia (muscular tissue under the skin that makes the scrotum appear wrinkly).^[11]

Having the scrotum and testicles situated outside the abdominal cavity may provide additional advantages. The external scrotum is not affected by abdominal pressure. This may prevent the emptying of the testes before the sperm were matured sufficiently for fertilization.^[12] Another advantage is it protects the testes from jolts and compressions associated with an active lifestyle. The scrotum may provide some friction during intercourse, helping to enhance the activity.^[13] The scrotum is also considered to be an erogenous zone.^[14]

A scrotum is present in all boreoeutherian land mammals except hippopotamuses, rhinoceroses, hedgehogs, moles, pangolins, and tapirs. The testicles remain in the body cavity in all other vertebrates, including cloacal animals.^[15]

Unlike placental mammals, some male marsupials have a scrotum that is anterior to the penis,^{[16][17][18][19]} which is not homologous to the scrotum of placental mammals,^[20] although there are several marsupial species without an external scrotum.^[21]

The scrotum is also absent in marine mammals, such as whales, dolphins, and seals,^[22] as well as in lineages of other land mammals, such as the afrotherians (elephants, aardvarks, etc.), xenarthrans (armadillos, anteaters, and sloths), and numerous families of bats and rodents.^[23][24]

• Scrotum of a bull
• Scrotum of a kangaroo
• Scrotum of a red deer
• Scrotum of a jaguar
• Scrotum of a camel
• Scrotum of a vervet monkey

A study has indicated that use of a laptop computer positioned on the lap can negatively affect sperm production.^[25][26]

• Retroperitoneal lymph node dissection
• Scrotal infusion, a temporary form of body modification
• Testicular self-examination

Books

• This article incorporates text in the public domain from page 1237 of the 20th edition of Gray's Anatomy (1918)
• Van De Graaff, Kent M.; Fox, Stuart Ira (1989). Concepts of Human Anatomy and Physiology. Dubuque, Iowa: William C. Brown Publishers. ISBN 978-0697056757.
• Elson, Lawrence; Kapit, Wynn (1977). The Anatomy Coloring Book. New York, New York: Harper & Row. ISBN 978-0064539142.
• "Gross Anatomy Image". Medical Gross Anatomy Atlas Images. University of Michigan Medical School. 1997. Retrieved 2015-02-23.
• Berkow, Robert (1977). The Merck Manual of Medical Information; Home Edition. Whitehouse Station, New Jersey: Merck Research Laboratories. ISBN 978-0911910872.