Vagina and Vulva of a Female Dog. Female dogs usually have a vagina which is extraordinarily long and deep, very muscular and capable of a great dilatation;. Female Dog Genitals & Dog Vulva & vaginal tumors. Generally, the abnormal postures that puppies adopt are due to the intersexuality and congenital fusion of the vulva. Dog vulva swelling is one of the best indications towards your dog being in heat, but can also point to allergic reaction or microbiotic infection. .