In "Reproductive Behaviour in Ungulates" Dr. Fraser says "The manner of penetration in the pig is unique; the male when mounted makes thrusting actions with the penis in semi-rotary actions. Only when the spiral-shaped penis lodged tightly in the firm fold does the action stop and ejaculation commences. It is clear, in fact, that the locking of the penis in the cervix acts as the essential stimulus to ejaculation in the boar." He includes a diagram of this connection mechanism.
A boar has a corkscrew-shaped penis wich fits into the corkscrew shaped cervix canal of the sow, thereby restricting backflow of semen during mating - which takes 10-30 minutes. In both cases the spiral takes the form of a "left-hand thread".
Parts of the Boar Penis:
The free part or tip is called the glans, the main section is called the body. The penis attaches to the ischial arch of the pelvis by 2 roots called the crura, which can be seen in this mounted specimen.
Erectile Function in the Boar:
This mounted penis is in the erect state - produced post-mortem by injecting the veins with embalming fluid, then tying them off to maintain pressure. This was done in order to demonstrate the coiling of the tip [glans] of the penis which is most marked during erection [in order to lock into the cervix of the sow and produce a seal against backflow of semen]. The non-erect penis is only marginally smaller, because, as with most ungulates, a pig's penis is composed of fibroelastic tissue to combine flexibility [it has to be able to bend to enter the female pig's vagina during mating] with penetration power. When artifical insemination was first developed in swine in the 1960s, it was usual to use a catheter with a coiled tip to give the same sealing effect.
The porcine penis shown here belonged to a boar of mine called Septimus [named after the famous veterinary anatomist Septimus Sisson]. After his death [the boar, not the anatomist!] I collected this specimen from the abattoir for use in my research which led to the publication of my book "Animal Breeding and Infertility".
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