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

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

In the scrotum, together with each testicle also is the epididymis, the initial part of the ductus deferens, nerves, blood vessels and lymphatics, and covering layers (read below).

Each testicle weighs approximately 0.7 - 1 ounce (20 - 30 grams). It is around 1.6 - 2 inches (4 - 5 cm) long and approximately 1 - 1.4 inches (2.5 - 3.5 cm) wide in the sagittal plane. 

The testicles each have two poles, two surfaces, and two margins:

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

The outer surfaces of testicles are covered by a thick fibrous connective tissue layer called tunica albuginea. Five more covering layers enclose the testicles.

Covering layers

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

Moving from the innermost to the outermost, the covering layers are:

• Tunica vaginalis testis - a serous layer, contains two sublayers (parietal and visceral), and between both is a small cavity that contains a tiny amount of serous fluid; the visceral layer is fused with the tunica albuginea;
• Internal spermatic fascia - a thin connective tissue layer, derived from the transversalis fascia, fused with the parietal layer of the tunica vaginalis testis;
• Cremaster muscle - formed by fibers of the internal abdominal oblique muscle and transversus abdominis muscle;
• Cremasteric fascia - formed by fibers of the external abdominal oblique muscle aponeurosis;
• External spermatic fascia - a thin fibrous membrane that developed from the superficial fascia of the abdominal wall.