. Chordate morphology. Morphology (Animals); Chordata. collagenous fibers which continue into bone as Shorpey's fiber Figure 8-49. Section of a mammalian tooth set in the jaw. (After Ham, 1957) opening of the cup. The dental lamina at this stage has a second generation of tooth germs extending down from it medial to the initial tooth germs. The enamel-producing epithelium is bell-shaped and formed of columnar ameloblasts or ganoblasts. The amelo- blasts induce the formation of odontoblasts in the adjacent dermal papilla, and these then produce the first layer of dentinal material, a soft fibro
. Chordate morphology. Morphology (Animals); Chordata. collagenous fibers which continue into bone as Shorpey's fiber Figure 8-49. Section of a mammalian tooth set in the jaw. (After Ham, 1957) opening of the cup. The dental lamina at this stage has a second generation of tooth germs extending down from it medial to the initial tooth germs. The enamel-producing epithelium is bell-shaped and formed of columnar ameloblasts or ganoblasts. The amelo- blasts induce the formation of odontoblasts in the adjacent dermal papilla, and these then produce the first layer of dentinal material, a soft fibrous material called preden- tine. The fibers of the odontoblasts extend between columns of the predentine. The appearance of the predentine next to the basal membrane of the ameloblasts induces the forma- tion of enamel. The soft pre-enamel material accumulates at the base of each ameloblast as a Tome's process; either this material is secreted through the basement membrane or that part of the cell containing it breaks down (merocrine secretion). As the ameloblasts move away from the secreted pre-enamel, new layers of Tome's processes appear and the long wavy and spiraled column is produced. The produc- tion of the soft material is periodic as is its calcification; this periodism produces the cross lines of Retzius seen in the rods. Inside of the enamel-dentine interface, the dentine is laid down in layers toward the pulp cavity, first as a soft pre- dentine and later as a calcified, hard dentine. Dentinal tubules containing the processes of the odontoblast are left behind as this process continues, and the processes elongate as the cells move further and further from the interface. The tooth structure of vertebrates can now be reviewed beginning with the fishes. Agnath fishes The agnath fishes are unique in that they do not have teeth of the gnathostome type. Some of the anaspids per- haps had small denticles similar to those of the body armor on the tooth plate in the floor of
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