There are between sixty and seventy teeth resembling incisors on the dental plate. The whole seem to be in a state of perennial renewal to compensate for wear and tear. As those of the front row are broken or worn down, the next succeeding row occupies the frontal position. The teeth are deeply set in the bony base of the inverted palate, or rather obtrude but slightly above the surface, their office being to break down and grind to powder flinty food. The outward and visible teeth of the male are apparently given as weapons of defence, since they do not occur in the female, which has four back teeth. From their prominent position the teeth of the male must also be used for grasping and levering or pulling steadfast limpets from rocks. They needs must be hard and have strength as well as science at the back of them, for a limpet can resist a pulling force of nearly 2000 times its own weight. The sutures of the jaws of the fish enable it to accommodate its grip to the various sizes of limpets, and to take a fair and square hold, while the lower jaw seems to act as a fulcrum when the leverage is applied. But the exterior jaws and teeth are devoid of interest, compared with the interior set, which form an ideal pulverising apparatus. To those who are versed in ichthyology, these are known as pharyngeal teeth, because they are connected with the pharynx. Such teeth are present in some form or other in all true fish, but usually in a degraded form. In the rainbow and parrot fish they are highly specialised, otherwise the pulverisation of the hard shell of molluscs would be impossible. The interior of the mouth of certain species of the shark family, given specially to a diet of oysters, is thickly set with a series of uniformly diffused minute teeth, and another fish of these seas has a gizzard composed of an intensely tough material, lined with membrane resembling shark's skin. This fish swallows cockles and such like molluscs whole, and grinds them in its gizzard.