A pair of glands that produce up to 70% of semen. They are located in front of the rectum, near the bladder, and they look like flattened rabbit ears that are anchored in the top middle part of the prostate gland. As they sit in the male body, each seminal vesicle is 3 to 5 cm in length and 1 cm in diameter. However, when they are uncoiled, they are roughly 10 cm in length. They are composed of 3 layers and produce a gel-like liquid that nourishes semen and helps increase the pH of the vagina so sperm can survive. The fluid they produce contains fructose to help provide a source of energy for sperm, as well as proteins, enzymes, vitamin C, and prostaglandins. They also produce an essential seminal vesical protein called semenogelin which forms a gel-like matrix that encases sperm during ejaculation. The seminal vesicles contract during the first part of ejaculation in order to expel their fluid into the urethra, where it is then shot out the end of the penis as the major component of semen.