The jaw of a shortfin mako shark. Cartilaginous fishes such as sharks and rays have one set of oral jaws made mainly of cartilage; unlike bony fishes, they do not have pharyngeal jaws. Generally fish jaws are articulated and oppose vertically, comprising an upper and lower jaw. Cartilaginous fishes grow multiple sets of ordered teeth, replacing them as they wear.Photograph: Didier Descouens