In human male

anatomy Anatomy () is the branch of morphology concerned with the study of the internal structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old scien ...

, the radix () or root of the penis is the internal and most proximal portion of the

human penis In Human body, human anatomy, the penis (; : penises or penes; from the Latin ''pēnis'', initially 'tail') is an external sex organ (intromittent organ) through which males urination, urinate and ejaculation, ejaculate, as Penis, on other anim ...

that lies in the

perineum The perineum (: perineums or perinea) in placentalia, placental mammals is the space between the anus and the genitals. The human perineum is between the anus and scrotum in the male or between the anus and vulva in the female. The perineum is ...

. Unlike the pendulous body of the penis, which is suspended from the pubic symphysis, the root is attached to the pubic arch of the

pelvis The pelvis (: pelves or pelvises) is the lower part of an Anatomy, anatomical Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also c ...

and is not visible externally. It is triradiate in form, consisting of three masses of erectile tissue; the two diverging crura, one on either side, and the median bulb of the penis or urethral bulb. Approximately one third to one half of the penis is embedded in the pelvis and can be felt through the

scrotum In most terrestrial mammals, the scrotum (: scrotums or scrota; possibly from Latin ''scortum'', meaning "hide" or "skin") 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 ...

and in the perineum.

Structure

The root of the penis begins directly below the bulbourethral glands, or ''Cowper glands'', and consists of three long masses of tissue; the bulb and the crura. The bulb of the penis is an enlarged mass of erectile tissue that is located in the midline of the root and is traversed by the male urethra. It continues as a long cylindrical body on the ventral aspect of the shaft called corpus spongiosum. The left and right crura are located laterally on the two sides of the bulb and are attached to the ischiopubic arch. They continue into the dorsal aspect of the shaft forming the two corpora cavernosa that are separated by the septum of the penis. During arousal, the root and the corpora cavernosa engorge with blood and become rigid (

erection An erection (clinically: penile erection or penile tumescence) is a Physiology, physiological phenomenon in which the penis becomes firm, engorged, and enlarged. Penile erection is the result of a complex interaction of psychological, neural, ...

). Meanwhile, the corpus spongiosum remains pliable making the urethra a viable channel for

semen Semen, also known as seminal fluid, is a bodily fluid that contains spermatozoon, spermatozoa which is secreted by the male gonads (sexual glands) and other sexual organs of male or hermaphrodite, hermaphroditic animals. In humans and placen ...

during

ejaculation Ejaculation is the discharge of semen (the ''ejaculate''; normally containing sperm) from the penis through the urethra. It is the final stage and natural objective of male sexual stimulation, and an essential component of natural conception. ...

Muscles

There are four muscles associated with the root of the penis; a pair of

ischiocavernosus The ischiocavernosus muscle (erectores penis ''or'' erector clitoridis in older texts) is a muscle just below the surface of the perineum, present in both men and women. Structure It arises by tendinous and fleshy fibers from the inner surface of ...

and a pair of bulbospondiosus muscles. Each crus is covered by the ischiocavernosus muscle which helps maintain an

by contracting to force blood from the crura into the corpora cavernosa. The bulb is surrounded by the bulbospongiosus muscle which contracts to help empty the urethra of any residual semen and urine. It also helps maintain the erection by increasing the pressure in the bulb. During orgasm, the muscles surrounding the root contract involuntarily pushing the semen towards the urinary meatus.

Fascia

Each erectile tissue has fascial coverings, or bands of

connective tissue Connective tissue is one of the four primary types of animal tissue, a group of cells that are similar in structure, along with epithelial tissue, muscle tissue, and nervous tissue. It develops mostly from the mesenchyme, derived from the mesod ...

, which surround and support them. The root of the penis lies in the perineum between the perineal membrane, or ''inferior fascia of the

urogenital diaphragm Older texts have asserted the existence of a urogenital diaphragm, also called the triangular ligament, which was described as a layer of the pelvis that separates the deep perineal sac from the upper pelvis, lying between the inferior fascia of ...

'', and the fascia of Colles, the deeper layer of the superficial perineal fascia.

Ligaments

In addition to being attached to the fasciæ and the pubic ramus, the root is bound to the front of the pubic symphysis by the fundiform and suspensory ligaments. * The fundiform ligament springs from the front of the sheath of the

rectus abdominis The rectus abdominis muscle, () also known as the "abdominal muscle" or simply better known as the "abs", is a pair of segmented skeletal muscle on the ventral aspect of a person, person's abdomen. The paired muscle is separated at the midline b ...

and the linea alba; it splits into two fasciculi which encircle the root of the penis. * The upper fibers of the suspensory ligament pass downward from the lower end of the linea alba, and the lower fibers from the pubic symphysis; together they form a strong fibrous band, which extends to the upper surface of the root, where it blends with the fascial sheath of the organ.

Images

File:Cunningham's Text-book of anatomy (1914) (20629645520).jpg, Root of the penis File:Cunningham's Text-book of anatomy (1914) (20630878319).jpg, Lateral cross-section of the male pelvis and its contents.

References