The woman is on all-fours, taking her weight on her forearms. The man kneels behind her, and enters her from behind, controlling the movement with his hips. This classic position will give both partners a great deal of pleasure, as the deep penetration will not only stimulate the vaginal walls, but also the G spot. The Dog will appeal to men who like to take the dominant role during sex and to women who like deep penetration and a high level of stimulation. However, some women may feel demeaned by the submissive role, or may feel pain, in which case there are plenty more positions to chose from!
Kamasutra described this posture as below :
When a woman stands on her hands and feet like a quadruped, and her lover mounts her like a bull, it is called the `congress of a cow’. At this time everything that is ordinarily done on the bosom should be done on the back.
Human love & sex 