Image Caption : Male Pelvis Showing Flaccid Penis: Medical visualization of the male pelvic region with an erect penis, also visible are the testicles, pelvis, femurs, and surrounding musculature. There are three columns of erectile tissue in the penis: at the top (or dorsal side) of the penis are the two corpora cavernosa, and at the bottom (or ventral side) is the corpus spongiosum. Upon arousal, the arteries that supply the penis dilate and allow blood to fill the three spongy erectile tissue columns, causing it to lengthen and stiffen. The engorged erectile tissue presses against penile veins, preventing blood from flowing back out of the penis.
The penis, the male copulatory organ, is a cylindrical pendant organ located anterior to the scrotum and functions to transfer sperm to the vagina. The penis consists of three columns of erectile tissue that are wrapped in connective tissue and covered with skin. The two dorsal columns are the corpora cavernosa. The single, midline ventral column surrounds the urethra and is called the corpus spongiosum.
The penis has a root, body (shaft), and glans penis. The root of the penis attaches it to the pubic arch, and the body is the visible, pendant portion. The corpus spongiosum expands at the distal end to form the glans penis. The urethra, which extends throughout the length of the corpus spongiosum, opens through the external urethral orifice at the tip of the glans penis. A loose fold of skin, called the prepuce, or foreskin, covers the glans penis.
National Cancer Institute / NIH
The human penis is an external male intromittent organ that additionally serves as the urinal duct. The main parts are the root (radix); the body (corpus); and the epithelium of the penis including the shaft skin and the foreskin covering the glans penis. The body of the penis is made up of three columns of tissue: two corpora cavernosa on the dorsal side and corpus spongiosum between them on the ventral side. The human male urethra passes through the prostate gland, where it is joined by the ejaculatory duct, and then through the penis. The urethra traverses the corpus spongiosum, and its opening, the meatus (/miːˈeɪtəs/), lies on the tip of the glans penis. It is a passage both for urination and ejaculation of semen.
The penis and many of its associated structures are homologous to the vagina and its associated structures. For example, the glans penis (the head of the penis) is homologous to the clitoris. An erection is the stiffening and rising of the penis, which occurs during sexual arousal, though it can also happen in non-sexual situations. The most common form of genital alteration is circumcision, removal of part or all of the foreskin for various cultural, religious and, more rarely, medical reasons. There is controversy surrounding circumcision.
While results vary across studies, the consensus is that the average erect human penis is approximately 12.9–15 cm (5.1–5.9 in) in length with 95% of adult males falling within the interval 10.7–19.1 cm (4.2–7.5 in). Neither age nor size of the flaccid penis accurately predicts erectile length.
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