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A bulbourethral gland, also called a Cowper's gland for English anatomist William Cowper, is one of two small exocrine glands in the reproductive system of many male mammals (of all domesticated animals, they are only absent in the dog). They are homologous to Bartholin's glands in females. The bulbouretheral glands are responsible for producing pre-ejaculate, a fluid secreted during sexual arousal neutralising the acidity of the urethra in preparation for the passage of sperm cells. 
|Artery||Artery of the urethral bulb|
Bulbourethral glands are located posterior and lateral to the membranous portion of the urethra at the base of the penis, between the two layers of the fascia of the urogenital diaphragm, in the deep perineal pouch. They are enclosed by transverse fibers of the sphincter urethrae membranaceae muscle.
The bulbourethral glands are compound tubulo-alveolar glands, each approximately the size of a pea in humans. In chimpanzees, they are not visible during dissection, but can be found on microscopic examination. In boars, they are up to 18 cm long and 5 cm in diameter. They are composed of several lobules held together by a fibrous covering. Each lobule consists of a number of acini, lined by columnar epithelial cells, opening into a duct that joins with the ducts of other lobules to form a single excretory duct. This duct is approximately 2.5 cm long and opens into the bulbar urethra at the base of the penis. The glands gradually diminish in size with advancing age.[unreliable source]
The bulbourethral gland contributes up to 4 ml of fluid during sexual arousal. The secretion is a clear fluid rich in mucoproteins that help to lubricate the distal urethra and neutralize acidic urine which remains in the urethra.
According to one preliminary study, the bulbourethral gland fluid does not contain any sperm, whereas another study showed some men did leak sperm in potentially significant quantities (in a range from low counts up to 50 million sperm per ml) into the pre-ejaculatory fluid, potentially leading to conception from the introduction of pre-ejaculate. However, the sperm source is a residual or pre-ejaculatory leak from the testicles into the vas deferens, rather than from the bulbourethral gland itself.
- Mark McEntee (December 2, 2012). Reproductive Pathology of Domestic Mammals. Elsevier Science. p. 333. ISBN 978-0-323-13804-8. Retrieved August 20, 2013.
- Jeffrey H. Schwartz (1988). Orang-utan Biology. Oxford University Press. p. 92. ISBN 978-0-19-504371-6. Retrieved August 20, 2013.
- Gray's Anatomy, 38th ed., p 1861.
- Killick, S. R; Leary, C; Trussell, J; Guthrie, K. A (2010). "Sperm content of pre-ejaculatory fluid". Human Fertility. 14 (1): 48–52. doi:10.3109/14647273.2010.520798. PMC 3564677. PMID 21155689.
- Zukerman, Z; Weiss, D. B; Orvieto, R (2003). "Short Communication: Does Preejaculatory Penile Secretion Originating from Cowper's Gland Contain Sperm?". Journal of Assisted Reproduction and Genetics. 20 (4): 157–159. doi:10.1023/A:1022933320700. PMC 3455634. PMID 12762415.