Concept
Canine reproduction is the process of sexual reproduction in domestic dogs, wolves, coyotes and other canine species. As with all mammals, a dog's penis is made up of three pieces of erectile tissue. These are the two corpora cavernosa and the singular corpus spongiosum which continues in the glans. A notable difference from the human penis is that the visible part during an erection consists entirely of the glans. The Retractor muscle is attached at the shaft of the penis. It is a paired smooth muscle that is used to retract the penis back into the sheath. A dog's glans consists of two sections: Behind the lower, long part (pars longa glandis) lies the "knot" (Bulbus glandis) which expands only after penetrating the vagina and causes the male dog to remain inside the bitch ("Tie") for some time after ejaculation (typically between 15 and 30 min). This increases the chance of fertilisation and prevents, albeit for a short time, other suites from mating with a particular female. Behind the knot the penis is very flexible in the horizontal direction allowing the male to unmount while remaining tied. The shaft of a dogs penis is not visible, even during an erection; however its pathway can be felt starting at the knot passing between the hind legs and carrying on up to the anus. Inside the corpus spongiosum lies the baculum. This allows the male dog to enter into the vagina before the erectile tissue is swollen. The urethra is located inside of a downward facing groove on the baculum and ends at the tip of the penis (urethral process). During an erection a small dip just above the urethral process can be seen. This is because the skin at the tip of the penis is connected via cartilage to the baculum. When the erectile tissue swells, the size of the baculum and connective tissue remains constant, pulling back the skin at the tip. The penile sheath entirely surrounds the glans while not erect. The back part is intergrown with the abdominal skin. The front part, almost reaching to the navel, is free.