. The chordates. Chordata. 42 Basic Structure of Vertebral* The crown of the tooth develops first. As the tooth grows, it in- creases in length as well as in thickness, adding first the neck region and later the root. The opening into the pulp-cavity becomes narrower as the root elongates until finally only a minute foramen remains to admit blood-vessels and nerves. The nerves, branches of the fifth cranial (trigeminal) nerves, grow into the pulp and each terminates in deli- cate fibrils which are intimately related to the odontoblast cells. The layer of cement is the last part of the tooth to
. The chordates. Chordata. 42 Basic Structure of Vertebral* The crown of the tooth develops first. As the tooth grows, it in- creases in length as well as in thickness, adding first the neck region and later the root. The opening into the pulp-cavity becomes narrower as the root elongates until finally only a minute foramen remains to admit blood-vessels and nerves. The nerves, branches of the fifth cranial (trigeminal) nerves, grow into the pulp and each terminates in deli- cate fibrils which are intimately related to the odontoblast cells. The layer of cement is the last part of the tooth to develop. The cement is produced by bone-forming cells (osteoblasts) derived from connective tissue external to the original tooth-germ. Eventually the bone of which the jaw is constituted fills in closely around the root of the tooth, form- ing a bony pocket or alveolus in which the tooth is firmly held in place. The eruption (, the piercing of the gum and emerging of the crown into the oral cavity) of the milk-teeth of man usually begins in ENAMEL PULP. _—AMELOBLAST LAYER — ENAMEL . £--ODONTOBLAST LAYER SB— PULP CAVITY TEMPORARY TOOTH Fig. 38. A section of the jaw of a nine-month human embryo, showing a developing canine tooth. The enamel-organ of the permanent incisor is seen on the lingual side of the milk-tooth. (After Corning. 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 these illustrations may not perfectly resemble the original Rand, Herbert W. (Herbert Wilbur), 1872-1960. Philadelphia : Blakiston
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