Many big cats such as lions, tigers, leopards and jaguars cannot purr because of a strip of cartilage that runs from the hyoid bones to the skull. The only big cat that purrs but cannot roar is the cheetah, which biologists place in a genus on its own, Acinonyx.
Smaller cats such as the ocelot, bobcat, cougar and lynx are able to purr. Purring ability is one of the major factors that separates the two main genera of cats, Felis and Panthera. Purring is enabled by delicate bones that connect the back of the tongue to the base of the skull.