Urethral sponge

The urethral sponge is a spongy cushion of tissue, found in the lower genital area of females, that sits against both the pubic bone and the vaginal wall, and is around the urethra.
Functions.
The urethral sponge is made of erectile tissue; during arousal, it becomes swollen with blood, and squeezes the urethra, helping to stop urination during sexual activity (along with the pubococcygeus muscle).
Female ejaculation.
Also, the urethral sponge has the Skene's glands, which might be used in female ejaculation.
Sexual stimulation.
The urethral sponge is around sensitive nerve endings, and can be stimulated through the front wall of the vagina. Some women have had strong pleasure from stimulation of the urethral sponge, but others have found the feeling to be not good, as irritating. The urethral sponge is around the clitoral nerve, and since the two are so closely inter-connected, stimulation of the clitoris may stimulate the nerve endings of the urethral sponge and vice versa. Some women enjoy the rear-entry position of sexual intercourse for this reason, because the penis is often angled slightly downward and can stimulate the front wall of the vagina, and then also the urethral sponge.
Relation with the G-spot.
The urethral sponge is an area in which the G-spot (Gräfenberg Spot) may be found. Although the G-spot may exist, it has been doubted by some researchers. A team at The King's College of London, in a big study on the G-spot's existence in recent years, and having 1,800 women, found no proof that the G-spot exists. The authors of the study had stated that the "G-spot" may be a figment (thought) of people's imagination, which has been encouraged by magazines, sex therapists and suggestive therapeutics. However, some other studies, using ultrasound, have found physiological evidence of the G-spot in women who report having orgasms during intercourse.