Clitoris and the penis - differentiation

 [This information needs a citation or reference.] The clitoris and penis are generally the same anatomical structure, although the distal portion (or opening) of the urethra is absent in the clitoris of humans and most other animals. The idea that males have clitorises was suggested in 1987 by researcher Josephine Lowndes Sevely, who theorized that the male corpora cavernosa (a pair of sponge-like regions of erectile tissue which contain most of the blood in the penis during penile erection) are the true counterpart of the clitoris. She argued that "the male clitoris" is directly beneath the rim of the glans penis, where the frenulum of prepuce of the penis (a fold of the prepuce) is located, and proposed that this area be called the "Lownde's crown." Her theory and proposal, though acknowledged in anatomical literature, did not materialize in anatomy books.[36] Modern anatomical texts instead show that the clitoris displays a hood that is the equivalent of the penis's foreskin, which covers the glans, and a shaft that is attached to the glans; the male corpora cavernosa are homologous to the corpus cavernosum clitoridis (the female cavernosa); the corpus spongiosum is homologous to the vestibular bulbs beneath the labia minora, and the scrotum is homologous to the labia minora and labia majora.[37]

Upon anatomical study, the penis can be described as a clitoris that has been mostly pulled out of the body and grafted on top of a significantly smaller piece of spongiosum containing the urethra.[37] With regard to nerve endings, the human clitoris's estimated 8,000 or more (for its glans or clitoral body as a whole) is commonly cited as being twice as many as the nerve endings found in the human penis (for its glans or body as a whole), and as more than any other part of the human body.[3] These reports sometimes conflict with other sources on clitoral anatomy or those concerning the nerve endings in the human penis. For example, while some sources estimate that the human penis has 4,000 nerve endings,[3] other sources state that the glans or the entire penile structure have the same amount of nerve endings as the clitoral glans,[38] or discuss whether the uncircumcised penis has thousands more than the circumcised penis or is generally more sensitive.[39][40]

Some sources state that in contrast to the glans penis, the clitoral glans lacks smooth muscle within its fibrovascular cap and is thus differentiated from the erectile tissues of the clitoris and bulbs; additionally, bulb size varies and may be dependent on age and estrogenization.[24] Though the bulbs are considered the equivalent of the male spongiosum, they do not completely encircle the urethra.[24]

The thin corpus spongiosum of the penis runs along the underside of the penile shaft, enveloping the urethra, and expands at the end to form the glans. It partially contributes to erection, which are primarily caused by the two corpora cavernosa that comprise the bulk of the shaft; like the female cavernosa, the male cavernosa soak up blood and become erect when sexually excited.[41] The male corpora cavernosa taper off internally on reaching the spongiosum head.[41] With regard to the Y-shape of the cavernosa – crown, body, and legs – the body accounts for much more of the structure in men, and the legs are stubbier; typically, the cavernosa are longer and thicker in males than in females.