the saggital crest is a bony structure on the top and back of the skull of some carnivorous mammals, where the temporalis muscle (one of the main muscles responsible for chewing) attaches to the sides of the skull.
generally the larger the crest is, the larger the mastication muscle of the animal to which it belongs.
the illustration above is the skull of a fisher - a member of the mustelid family, along with weasels, otters, wolverines etc.
photo credit for the second pic is attributed to Douglas H. Domedion via Wikipedia