Both the median and the paired fins are supported by an internal skeleton, consisting (i.) of a series of cartilaginous or bony, rod-like radial elements or pterygiophores, for the support of the inner or proximal portion of the fins, and (ii.) of a series of horny fibres, or bony dermal fin-rays, which fulfil a like function for the outer or distal portion. The radial elements, however, are never visible externally, even when, as in most Elasmobranchs, they support the greater part of the fins, inasmuch as they are invested by the fin-muscles and the skin; and in the same group, where horny fibres complete the fin-skeleton, they too are covered by the spinose skin, and hence offer no external evidence of their existence. In the Teleostomi a marked reduction in the number and length of the radial elements of the paired fins, and the insinking of those pertaining to the median fins into the adjacent muscles of the body-wall, leaves the dermal fin-rays, with their thin covering of transparent and usually scaleless skin, as obvious features in the external appearance of the Fish, and apparently as the sole support of the fins. The dermal fin-rays of the Teleostomi exhibit an obvious distinction into spines and soft rays (Fig. 93, A). The former are stout, rigid, and unbranched structures, pointed at their free distal ends, which, in numbers differing in different genera and species, support the anterior portions of the dorsal, anal, and pelvic fins. {159}Soft rays are flexible, branched distally, and generally exhibit a transversely-jointed structure; when present in conjunction with spines they invariably lie behind the latter. The presence of both kinds of fin-rays, or of soft rays only, is one of the more obvious distinctions between the Teleostean groups of the Acanthopterygii and the Malacopterygii, of which the Perch and the Salmon respectively are well-known examples. Powerful spines are frequently developed in front of the dorsal fin in many living and extinct Elasmobranchs, and, under the general term of "ichthyodorulites," constitute the sole fossil remains of many extinct Devonian and Carboniferous genera.