A horses wolf teeth are vestiges of premolars from prehistoric horses. They are located behind the incisors and in front of the other premolars, usually only in the upper jaw. I learned about wolf teeth when I was told my young horse, Leo, was going to need to have his removed.
Veterinarians often recommend these teeth be removed in riding horses because they are positioned in such a way that the bit could catch on the teeth, hurting the horses mouth. Because the teeth no longer have a use in our modern horses, the removal does not cause any issues. Also, the procedure can be done on location and only takes about twenty minutes - so it is relatively low cost and quite safe!
Here is an image of where the wolf teeth are located in a horse's mouth:
This image is borrowed from: http://www.kbrhorse.net/hea/float.html
And for those who don't mind the sight of blood...unlike myself - here is a photo of Leo's pulled wolf teeth, demonstrating how small they are (for a horse):
Leo has recovered very successfully from this small procedure and is chewing on everything, per his usual self. :)
