. The elasmobranch fishes. Chondrichthyes. A. Young stage B. Older stage Fig. 37. Development of fin spine, Acanthias. (From Markert.) ct., core of cartilage; d., primary dentine; d.', secondary dentine; e., enamel; , enamel organ; ep., epidermis; fs., connective tissue fibers; od., odontoblast; pg., pigment. front of it and others behind it. Both of these sets of odontoblasts lay down dentine so that the fibers (fs.) come to lie between two layers of dentine. Finally the fibers themselves also give place to dentine. Hence a transverse section of this secondary dentine, taken at the base o
. The elasmobranch fishes. Chondrichthyes. A. Young stage B. Older stage Fig. 37. Development of fin spine, Acanthias. (From Markert.) ct., core of cartilage; d., primary dentine; d.', secondary dentine; e., enamel; , enamel organ; ep., epidermis; fs., connective tissue fibers; od., odontoblast; pg., pigment. front of it and others behind it. Both of these sets of odontoblasts lay down dentine so that the fibers (fs.) come to lie between two layers of dentine. Finally the fibers themselves also give place to dentine. Hence a transverse section of this secondary dentine, taken at the base of the spine where the sheath of fibers is closed into a ring, shows a heavy circle of secondary dentine like the broad band around the core of cartilage {d\ fig. 40); a similar trans- verse section taken toward the tip would indicate the layer of dentine as a crescent just back of the central Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Daniel, J. Frank (John Franklin), 1873-1942. Berkeley,Calif. , University of California press
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