The Penis is described as consisting of a root and body. The root consists of the bulb of the corpus spongiosum, which lies in the middle line in front of the anterior layer of the triangular ligament, and of the corpora cavernosa, which are attached at either side to the rami of the pubis and ischium. These three structures meet under the pubic arch, where they are fixed by strong connective-tissue bands, and fuse to form the body of the penis. They are further supported by a fascial suspensory ligament from the front of the pubis, and are so arranged that one of the corpora cavernosa occupies either side, while in a sulcus on the deep surface lies the corpus spongiosum, with the urethra embedded in it. Toward the point of the penis, howrever, the corpus spongiosum ascends, and, spreading out, forms the glans penis. The corpora cavernosa are surrounded by a fibrous envelope, the tunica albu-ginea, and are imperfectly separated from one another by the septum pectiniforme. They consist, like the corpus spongiosum, of cavernous tissue, and each presents, close to the septum, an artery to the corpus. In gonorrhceal affections the corpus spongiosum may be rendered indistensible, so that in erection of the penis it remains contracted, thus producing curvature of the organ. Superficially the organ is enveloped in a thin skin, wrhich, owing to the lax subcutaneous tissue, is very mobile. Thus it is necessary in performing circumcision to see that an excessive amount of skin is not pulled forward and removed. The subcutaneous tissue, traversed by the dorsal vein of the penis, is very lax, and becomes much swollen when cedematous or when extravasation of urine has occurred.
Under the subcutaneous tissue is the fascia penis, which is continuous with the fascia of Colles in the perineum. The prepuce is formed of a reduplication of the skin, which covers the glans and neck of the penis. It is attached on the under surface to the glans by the frcenum. Where the prepuce is long and so narrow that it cannot be retracted from the glans, the condition is known as phimosis. Where the prepuce, having been drawn back, forms a constriction round the base of the glans and cannot be returned, the condition is called paraphimosis. The lax tissue about the corona enables the Hunterian chancre to develop characteristically, with marked induration ; whereas on the glans the submucous tissue is practically absent, and the mucous membrane very adherent.
Certain congenital defects may occur in the penis. The cloaca is divided into an anterior urogenital canal, and a posterior rectum, by the coalescence of two lateral folds. The upper portion of the canal receives the ureters and forms the bladder, and the lower portion forms the prostatic and membranous portions, receives the ducts of Wolff and Mutter, and opens in front of the anus as the urogenital sinus. At the apex of this sinus a small genital tubercle appears, and on either side a genital fold, while posteriorly the sinus is separated from the rectum by the perineal septum. In the male the penis is formed from the genital tubercle, which elongates, while a furrow appears on its ventral aspect. This furrow deepens, the lateral margins curve round the groove and coalesce at the median raphe, and thus the spongy urethra is formed. This process of fusion proceeds from behind, forwards. By the coalescence of the genital folds, the scrotum is formed. In the female the tubercle forms the clitoris and the folds the labia majora, while the ducts of Miiller coalesce to form the uterus and vagina. Hypospadias, where the imperfect urethra opens on the ventral surface of the penis, may be complete, the urethra opening at the base of the penis, or the scrotum may even be cleft (the testicles partially descended or retained), and the urethra open behind it, the parts thus resembling the female organs (pseudo-hermaphroditism). In less severe cases the urethra may open under the glans or body of the penis. In epispadias the penis has either been cleft from above or has become twisted. Usually the organ is badly developed, and the severer forms are frequently associated with extroversion of the bladder.
The penis is supplied by branches of the internal pudic artery, the blood returning directly or through the dorsal vein to the prostatic plexus. The nerves are derived from the internal pudic and hypogastric plexus, the latter supplying the erectile tissue. The pudic supplies the greater part of the skin, and also the muscles and mucous membrane of the urethra. Thus urethral irritation frequently gives rise to erection of the penis (e.g., gonorrhoeal chordee), and a similar result may be caused by the collection of smegma under the prepuce, while it is possible that such forms of irritation may also give rise to spasm of the urethral muscles.