The horse's chestnuts are likely to be vestigial remains of the thumb pad
The horse's splint bones are vestigial remains of the 2nd and 4th metacarpal/metatarsal bones
A term that refers to a remaining part of something that is not (fully) developed. For example, the splint bones in the horse are the remains of much larger bones in the digit that were present in the horse's ancestors. It is therefore known as a vestigial bone.
