The male reproductive system consists of two parts: the internal and external genitalia. The internal genitalia consist of the gonads (testes), vas deferens (epididymis, vas deferens, ejaculatory ducts and urethra) and accessory glands (seminal vesicle glands, prostate gland, urethral bulb glands). The external genitalia include the penis and scrotum. I. Internal genitalia (a) gonads (testes) The testes are male gonads, one on each side, oval, 3-4 cm long, 2-3 cm wide and 1-2 cm thick in adults, each focusing on 10-15 grams. It is located in the scrotum. The left side is 1 cm lower than the right side. The main function is to produce sperm and androgens. (B) Vas deferens (including epididymis, vas deferens, ejaculatory duct and urethra) 1. Epididymis: It is attached to the testicle immediately above the outside and is 5-6 cm long. It is the main place for storing sperm and providing nutrition for sperm growth and maturation. 2.Vas deferens: The total length is about 40-50 cm. It goes up from the tail of the epididymis and enters the pelvis with the spermatic cord. It merges with the seminal vesicle excretory duct to form the ejaculatory duct. Epididymis: The spermatic cord is a pair of flat, round cords that extend from the upper end of the testis to the inguinal canal’s inner mouth. It consists of three layers of fascia outsourced by the vas deferens, testicular artery, tracheal plexus, nerve plexus, lymphatic vessels, etc. 3, ejaculatory duct: about 2 cm long, from the vas deferens and seminal vesicle excretory duct merged, through the prostate, opening in the urethra prostate department. 4, male urethra: both the urinary tract and seminal drainage duct. In adults, it is about 18 cm long and can be divided into three parts: the prostate, the membrane (both collectively called the posterior urethra) and the spongy part (anterior urethra). (iii) Accessory glands 1, the seminal vesicle gland: is a flat oval sac-shaped organ located behind the base of the bladder, function is to produce seminal plasma, is the main component of the composition of semen. 2, the prostate gland: chestnut-shaped, bottom up tip down, weighing about 20 grams. It is located below the bladder. Inside the beginning of the urethra segment. Function: It secretes a milky alkaline fluid (called prostatic fluid), which becomes seminal fluid by mixing with seminal plasma, urethral bulb gland fluid and sperm. 3. Urethral bulb gland: opens at the beginning of the spongy part of the urethra. Function: Secrete urethral bulb gland fluid and participate in the composition of semen. External genitalia 1, penis: adult penis is about 7-10 cm long, and can grow 1 times when erect. Divided into three parts: penis head, penis body and penis root. The skin of the penis is thin and easy to stretch, suitable for penile erection. The skin from the body to the neck of the penis is free and forms a ring-shaped fold around the head of the penis called the prepuce. The penis is composed of two penile corpus cavernosum and one urethral corpus cavernosum. The cavity of the corpus spongiosum is connected with blood vessels, and when the corpus spongiosum is filled with blood, the penis enlarges and becomes erect. 2. Scrotum: Located between the perineum and the penis, it contains the testicles. When the body temperature rises, the scrotum stretches, and when the body temperature drops, the scrotum contracts to keep the temperature inside the scrotum lower than the body temperature, which is especially important for sperm development and survival.