Scales,

Scales, modifications of the skin especially characteristic of fishes and reptiles. Those of lizards and serpents are due to folds of the epidermis, the outer or horny layer of which is in various degrees hardened. So the scales of the pangolin and of the beaver's tail, or those which cover the legs and toes of many birds, are epidermic. On the other hand, the scales of most bony fishes (Teleostei) and of the Dipnoi are developed from the under skin or dermis, and are thus comparable to the little bony plates which occur in the skin of not a few lizards, to the large bony 'scutes' of the crocodilians and many extinct reptiles, and to the armature of the armadillos. A third type of scale is represented by the skin-teeth or 'dermal denticles' of Elasmobranch fishes, for in these, as in the teeth of the mouth, the epidermis forms an external coating of enamel, while the bony core and base are developed from the dermis. To this type the hard scales of some Ganoids (e.g. the sturgeon, bony pike) and a few Teleosts are also to be referred. Dermal scales are of especial interest, for in a coalescence of these the 'investing bones' of the skull and shoulder-girdle had probably their origin. See FISHES, SKELETON.