This is swept into the open end of the fallopian tube and begins to move slowly down it. In tubal ligation, the fallopian tubes are surgically cut and their ends tied to prevent pregnancy. For fertilization to occur, sperm must be deposited in the vagina within a few days before or a day or two after ovulation. Sperm transfer is accomplished by copulation. Sexual excitation dilates the arterioles supplying blood to the penis.
Blood accumulates in three cylindrical spongy sinuses that run lengthwise through the penis.
The resulting pressure causes the penis to enlarge and erect and thus able to penetrate the vagina. Movement of the penis back and forth within the vagina causes sexual tension to increase to the point of ejaculation . Contraction of the walls of each vas deferens propels the sperm along. Fluid is added to the sperm by the seminal vesicles , Cowper's glands, and the prostate gland . The mixture of sperm and accessory fluids is called semen .