Mastiffs are powerful, heavily built dogs, with short muzzles, frequently protruding lower jaws, skulls raised above the eyes, ears erect or pendulous, pendulous upper lips, short coats and thin tails.
The entire body behind the shoulder-blades is uniformly coloured, with the exception of the feet; the anterior part of the body, including the fore legs, neck, and jaws, is white, the cheeks and ears being coloured.
Again, the adult Pentastomum shows no trace of appendages, unless the two pairs of chitinous hooks are to be regarded as the vestiges of jaws or ambulatory limbs.
Teeth and jaws probably referable to the Condylarthra have been obtained in European early Tertiary formations.
This piece of apparatus was introduced by William Morris in 1831, and consists of a long double link with closely-fitting jaws which, however, slide freely up and down.