In _Argyropelecus_ and in one or two deep-sea forms the vertebral column remains cartilaginous. [Illustration: From Parker & Haswell's _Text-book of Zoology_, by permission of Messrs. Macmillan & Co., Ltd. FIG. 23.--One of the radialia of the salmon, consisting of three segments, ptg¹, ptg², ptg³, and supporting a dermal fin ray. _D.F.R._] Apart from the ossification of the radialia which takes place in the adults of bony fishes there exist special supporting structures in the fins (paired as well as median) of all the gnathostomatous fishes and apparently in nature independent of the cartilaginous skeleton. These are known as dermal fin-rays.[34] Morphologically they are probably to be looked on (like placoid elements) as local exaggerations of the basement membrane. In their detailed characters two main types of dermal fin-ray may be recognized. The first of these are horny unjointed rays and occur in the fins of Selachians and at the edge of the fins of Teleostomes (well seen in the small posterior dorsal or "adipose" fin, particularly in Siluroids). The second type of dermal fin-ray is originally arranged in pairs and forms the main supports of the fin in the adult Teleost (fig. 23). The members of each pair are in close contact except proximally where they separate and embrace the tip of one of the radialia. The fin-rays of this second type are frequently branched and jointed: in other cases they form unbranched rigid spines. In the angler or fishing-frog (_Lophius_) the anterior rays of the dorsal fin become greatly elongated to form small fishing-rods, from which depend bait-like lures for the attraction of its prey. [Illustration: From Wiedersheim, _Verg. Anat. der Wirbeltiere_, by permission of Gustav Fischer. FIG. 24.--Chondrocranium of Salmon, seen from the right side. alsph, Alisphenoid. orbsph, Orbitosphenoid. basocc, Basioccipital. proot, Prootic. ekteth, Lateral ethmoid. psph, Parasphenoid. epiot, Epiotic. ptero, Pterotic. exocc, Exoccipital. socc, Supra occipital. fr, Frontal. sphot, Sphenotic. opisth, Opisthotic. vo, Vomer.]