. The chordates. Chordata. The Inner (Alimentary) Tube and Its Respiratory Derivatives 39 contains no living substance and is incapable of self-repair, but loss of dentine at the outer surface of the layer may be compensated for by deposition of additional dentine at the internal surface. Development of Teeth Teeth develop in much the same way in all vertebrates, but the process is necessarily more complex in the larger and more highly differentiated teeth. Naturally, the develop- ment of human teeth has been especially care- fully studied. A brief account of it may well serve the present purp
. The chordates. Chordata. The Inner (Alimentary) Tube and Its Respiratory Derivatives 39 contains no living substance and is incapable of self-repair, but loss of dentine at the outer surface of the layer may be compensated for by deposition of additional dentine at the internal surface. Development of Teeth Teeth develop in much the same way in all vertebrates, but the process is necessarily more complex in the larger and more highly differentiated teeth. Naturally, the develop- ment of human teeth has been especially care- fully studied. A brief account of it may well serve the present purpose. When the human embryo has attained a length of about 11 mm.—that is, by the end of the sixth week of development—the ecto- dermal epithelium covering the jaws grows rapidly into the underlying connective tissue to form adental ridge or lamina extending parallel to the edge of each jaw. The lamina is formed by multiplication of cells in the deep- est layer (stratum germinativum) of the ectodermal epithelium which is continuous with the external epidermis (Fig. 35). As growth continues, the deep edge of the lamina (labial) lamina and an inner (lingual) lamina. 0, Fig. 34. Five odonto- blasts, from which Tomes's fibers extend up- ward into the dentine; from a tooth of a new- born cat. (After Prenant. Courtesy, Bremer: "A Text-Book of Histology," Philadelphia, The Blakis- ton Company.) divides into an outer With further growth,. C0RIUM BONY ALVEOLUS LINGUAL LAMINA ENAMEL ORGAN OF PERMANENT TOOTH Fig. 35. Diagrams of three stages in the development of a mammalian tooth as seen in sections of the jaw. The enamel-organ of the permanent tooth lies on the lingual side of that of the milk-tooth. (After O. Hertwig and Arey. Courtesy, Neal and Rand: "Chordate Anatomy," Philadelphia, The Blakiston Company.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of th
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