It has to be taken into account that the cat skull, in addition to having a smaller brain volume and thicker cranial bones than that of dogs, is also prognathous. This means that the lower face projects forward, rather in the manner of an animal's muzzle. In consequence, the cat jaw is substantially longer, relative to its width,than the dog jaw. A feature of the cat lower jaw is its retention ofa vestige of the "simian shelf," a bony region immediately behindthe incisors. To make it more obvioys, the simian shelf is a distinguishing characteristic of apes, which is of course absent in dogs.