<P> As with most tetrapods, canine copulation involves the male mounting the female from behind, a position that is referred to as "doggy style" but does not have a specifically known origin . When a male canine is interested in mounting a female, he will sniff the female's vulva . If the female is unreceptive, she may sit, lie down, snap, retreat, or otherwise be uncooperative . If the female is receptive, she will stand still and hold her tail to the side, a stance referred to as "flagging". The male will often continue examining the female's rear, before mounting her from behind while attempting penetration with his penis . </P> <P> At the time of penetration, the canine penis is not erect, and only able to penetrate the female because it includes a narrow bone called the "baculum", a feature of most placental mammals . When the male achieves penetration, he will usually hold the female tighter and thrust deeply . It is during this time that the male's penis expands and it is important that the bulbus gland is sufficiently far inside for the female to be able to trap it . Unlike human sexual intercourse, where the male penis commonly becomes erect before entering the female, canine copulation involves the male first penetrating the female, after which swelling of the penis to erection occurs, which usually happens rapidly . </P> <P> Male canines are the only animals that have a locking bulbus glandis or "bulb", a spherical area of erectile tissue at the base of the penis . During copulation, and only after the male's penis is fully inside the female's vagina, the bulbus glandis becomes engorged with blood . In coyotes, when the female's vagina subsequently contracts, the penis becomes locked inside the female . This is known as "tying" or "knotting". While characteristic of mating in most canids, the copulatory tie has been reported to be absent or very brief (less than one minute) in the African wild dog, possibly due to the abundance of large predators in its environment . </P> <P> When the penis is locked into the vagina by the bulbus glandis (when the stud is "tied"), thrusting behavior stops and the male will usually lift a leg and swing it over the female's back while turning around . The two stand with their hind ends touching and the penis locked inside the vagina while ejaculation occurs, decreasing leakage of semen from the vagina . After some time, typically between 5 and 20 minutes (but sometimes longer), the bulbus glandis disengorges, allowing the mates to separate . Virgin dogs can become quite distressed at finding themselves unable to separate during their first copulation, and may try to pull away or run . Dog breeders often suggest it is appropriate for handlers to attempt to calm the mating dogs if they show anxiety once this stage is reached . After mating, the male usually licks his penis and prepuce . </P>

Where does a male dog enter a female dog