The bulbus glandis (also called a bulb or knot) is an

erectile tissue Erectile tissue is tissue in the body with numerous vascular spaces, or cavernous tissue, that may become engorged with blood. However, tissue that is devoid of or otherwise lacking erectile tissue (such as the labia minora, vestibule, vagina and ...

structure on the penis of canid mammals. During mating, immediately before ejaculation the tissues swell up to lock ('' tie'') the male's penis inside the female. The locking is completed by circular muscles just inside the female's vagina; this is called "the knot" tightening thus preventing the male from withdrawing. The circular muscles also contract intermittently, which has the effect of stimulating ejaculation of sperm, followed by prostatic fluid, as well as maintaining the swelling of the penis and therefore the tie, for some time. For domestic dogs the tie may last up to half an hour or more, though usually less. When male canines are sexually excited, the bulbus glandis may swell up inside the

penile sheath Almost all mammal penises have foreskins or prepuces. In non-human mammals, the prepuce is sometimes called the penile sheath or preputial sheath. In koalas, the foreskin contains naturally occurring bacteria that play an important role in fer ...

, even if the dog has been neutered. The bulbus glandis also occurs in the penises of some

pinniped Pinnipeds (pronounced ), commonly known as seals, are a widely range (biology), distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals. They comprise the extant taxon, extant families Odobenidae (whose onl ...

s, including South American fur seals.

References

{{reflist Dog anatomy Dog breeding Mammal penis

See also

References