The Penis
This has two functions as both the copulatory organ and the external urethra. During copulation the erect penis can enter the female vagina (intromission), allowing the ejaculation of semen into or at the entry to the cervix.
The penis is normally flaccid but becomes erect prior to copulation.To carry out its function the penis includes an extrapelvic extension of the urethra along which urine and semen may pass. It is constructed of tissue that can become engorged with blood, resulting in erection.
The penis comprises the body (or shaft) and the two crura (the root of the penis), which are each attached to an ischium on either side of the bony pelvis (os coxae). The distal portion of the penis is extrapelvic and is covered by the prepuce; in most species the distal extremity of the penis is expanded as the glans penis. The urethra is a tube lying along the midline within the penis; it conducts either semen or urine as required. The prepuce is a cutaneous sheath that covers the free part of the non-erect penis.
15.2