The mare's reproductive system is similar to that of other female mammals, with some unique characteristics. The vagina is a muscular, tubular structure that extends from the vulva to the cervix.

I'm assuming you're looking for information on the anatomy of a horse's reproductive system, specifically the vagina. Here's some information:

The vagina of a mare is approximately 30-40 cm (12-16 inches) long and is lined with mucous membranes. It is surrounded by a pair of labia, which are the external folds of skin that protect the vulva. The vagina is also supported by a layer of connective tissue and muscles, including the vaginal muscle and the levator ani muscle.