The testicles or testes are the primary male reproductive glands that produce sperm and synthesize sex hormones called androgens.

Testes are oval-shaped main male reproductive system organs that both are placed in the sagittal axis close to each other in the scrotum. Both testicles are separated by the septum of the scrotum.

They develop on the posterior abdominal wall, but descend through the inguinal canal to the scrotum before birth.

Usually, the left testicle is located a little bit lower than the right. 

NOTE: testicles need to descend in the scrotum as spermatogenesis cannot happen at a body temperature, and spermatozoa cannot be produced. Spermatogenesis requires a temperature that is few degrees below body temperature.

Together with the testicles in the scrotum also are located epididymis, initial part of the ductus deferens, nerves, lymphatic and blood vessels, and covering layers.

They weigh approximately 20-30 grams. Testicles are 4-5 cm long and 2.5-3.5 cm wide in the sagittal plane. They are covered with a thick fibrous connective tissue layer called the tunica albuginea.

Testicles have two poles, two surfaces, and two margins:

  • Poles: superior and inferior;
  • Surfaces: medial and lateral;
  • Borders: anterior and posterior.

Both testis and epididymis have five covering layers above the tunica albuginea, which are formed during embryonic development when testicles descend in the scrotum as they also push other abdominal wall structures through the inguinal canal.

Moving from the innermost to the outermost layer, these are:

  • Tunica vaginalis testis - serous layer, contains two layers named the parietal and visceral layers, and between both is a small cavity that contains a small amount of serous fluid; the visceral layer is fused with the tunica albuginea;
  • Internal spermatic fascia - it is fused with the parietal layer of the tunica vaginalis testis;
  • Cremaster muscle - formed by the fibers of the internal abdominal oblique muscle and transversus abdominis muscle;
  • Cremasteric fascia - formed by the fibers of the external abdominal oblique muscle aponeurosis;
  • External spermatic fascia - developed from the superficial fascia of the abdominal wall.